SPECIES starting with "p"

 

Pinnularia divergentissima

  1. Striae with abrupt transition
  2. Valves linear to linear-lanceolate
  3. Apices subrostrate and obtusely rounded
  4. Raphe straight
  5. Proximal raphe ends closely spaced

Symmetrical biraphid - Pinnularia divergentissima is striking in appearance because of the abrupt transition from extremely radiate to extremely convergent striae. Valves are linear to linear-lanceolate with subrostrate and obtusely-rounded apices. Raphe branches are filiform and the proximal raphe ends are small and close to one another.


Pinnularia marchica

  1. Valves linear to elliptic-lanceolate
  2. Apices rostrate to slightly capitate
  3. Central area large, reaching valve margin
  4. Striae radiate near valve center

Symmetrical biraphid - Valves are linear to elliptic-lanceolate. The apices are rostrate to slightly subcapitate. Valves are 4-5 µm in width. The axial area is lanceolate, widening into a large central area that extends to the valve margin. Striae are radiate near the valve center and slightly convergent near the apices.


Pinnularia parvulissima

  1. Apices broadly rostrate to subcapitate
  2. Fascia present
  3. Proximal raphe ends closely placed
  4. Striae radiate in middle of valve
  5. Striae slightly convergent near apices

Symmetrical biraphid - Pinnularia parvulissima has broadly rounded, subcapitate ends. The central area is large with a broad, rhombic fascia. The fascia is variable in width in different specimens. The raphe is lateral. The proximal raphe ends are small and closely placed.


Pinnularia polyonca

  1. Valves triundulate
  2. Apices capitate
  3. Axial area broad, lanceolate
  4. Central fascia

Symmetrical biraphid - Valves are triundulate with the broadest portion in the middle. Apices are capitate. The axial area is broad and lanceolate, merging with a central transverse fascia.


Pinnularia saprophila

  1. Valves linear
  2. Apices capitate to slightly protracted
  3. Central area reaching the valve margin
  4. Striae radiate near the center

Symmetrical biraphid - Valves are linear, with capitate to slightly protracted apices. Valves are 5.2-6.7 µm in width. The axial area is lanceolate, widening into a large central area that reaches the valve margins. Striae are often slightly bent, radiate near the valve center and extremely convergent at the apices.


Placoneis abiskoensis

  1. Valves linear
  2. Valve margins parallel or weakly concave
  3. Apices rostrate to subcapitate
  4. Central area transverse
  5. Striae strongly curved

Symmetrical biraphid - Placoneis abiskoensis has relatively large linear valves, 33-46 µm in length. Margins are parallel or weakly concave margins. The apices are rostrate to subcapitate. The central area is large and transversely rectangular. Striae are strongly curved and radiate.


Placoneis elginensis

Navicula elginensis
Placoneis dicephala var. elginensis

  1. Valves elliptical-lanceolate
  2. Apices protracted, rostrate
  3. Central area round

Symmetrical biraphid - Valves are elliptical-lanceolate, with margins convex and apices protracted and rostrate. The central area is round central. Striae are indistinctly punctate, curved and radiate throughout the length of the valve.


Plagiotropis arizonica

  1. Valves large
  2. Areolae distinct
  3. Striae convergent and more widely spaced at valve center

Symmetrical biraphid - Valves are linear-lanceolate and large, greater than 110 µm in length. Striae are somewhat convergent and more widely spaced at the valve center. Areolae are distinct in LM and number 15-18 in 10 µm.


Plagiotropis lepidoptera var. proboscidea

  1. Valves medium
  2. Areolae very fine
  3. Striae parallel at valve center

Symmetrical biraphid - Valves are lanceolate and less than 110 µm long. A prominent keel carrying the raphe runs along the apical axis. Striae are parallel in the middle, becoming radiate towards the apices. Areolae are very fine and number 26-30 in 10 µm.


Planothidium abbreviatum

  1. Valves elliptic-lanceolate with subrostrate apices
  2. Raphe valve with transversely rectangular to elliptic central area
  3. Rapheless valve with rhomboid axial area
  4. Rapheless valve with hood
  5. Striae radiate

Monoraphid - Valves are elliptic-lanceolate with subrostrate apices. The raphe valve has a transversely rectangular to elliptic central area. The rapheless valve has a rhomboid axial area and asymmetric central area with a hood on the internal valve surface. The striae are radiate.


Planothidium apiculatum

  1. Valves elliptical-lanceolate with apiculate apices
  2. Valves 9.0-12.7 μm wide
  3. Rapheless valve with a hood

Monoraphid - Valves are elliptical-lanceolate with apiculate apices. The raphe valve has a large rhomboid or transversely elliptical central area. The rapheless valve has an asymmetrical central area, expanded at one side to the valve margin and containing a prominent hood . The striae are strongly radiate on the raphe valve and slightly radiate on the rapheless valve.


Planothidium biporomum

  1. Valves lanceolate with capitate to subrostrate apices
  2. Valves 5.4-7.0 μm wide
  3. Rapheless valve with a 'hood'

Monoraphid - Valves are lanceolate with capitate to subrostrate apices, 12-25 μm long, 5.4-7.0 μm wide. Rapheless valve has a linear-lanceolate axial area and an asymmetrical central area containing a hood on the internal valve surface. The striae are multiseriate, radiate throughout both valves, 12-15 in 10 μm.


Planothidium calcar

  1. Valves elliptical
  2. Central area asymmetric
  3. Hood present on both valves
  4. Central area reaches valve margins

Monoraphid - Valves are elliptical. The axial area is narrow and linear on the raphe valve; the axial area is narrow and rhomboid on the rapheless valve. The central area on both valves is asymmetric, expanded to the valve margins and contains a hood. The striae are fine and radiate throughout both valves.


Planothidium delicatulum

  1. Apices protracted and subrostrate
  2. Raphe valve with transversely elliptical or rectangular central area
  3. Rapheless valve lacks a central area
  4. Rapheless valve may have 2 middle, distant striae on one valve side

Monoraphid - Valves are lanceolate with protracted subrostrate apices. The raphe valve has a transversely elliptical or rectangular central area. The rapheless valve has a linear-lanceolate axial area and no distinguishable central area, or two middle striae on one side of the raphe can be slightly more distant for each other than from the other striae.


Planothidium dubium

  1. Valves linear-elliptical with variable apices
  2. Valves 4.0-8.5 μm wide
  3. Rapheless valve with a shallow depression
  4. Axial area on rapheless valve narrow linear

Monoraphid - Valves are linear-elliptical with rostrate, subrostrate or narrowly subcapitate apices. The raphe valve has a linear axial area and transversely rectangular central area. The rapheless valve has a narrow, linear axial area. The asymmetric central area on the rapheless valve contains a shallow depression on the internal valve surface.


Planothidium frequentissimum

  1. Valves lanceolate to elliptical with rounded or slightly drawn-out apices
  2. Valves 3-6 μm wide
  3. Rapheless valve with a hood

Monoraphid - Valves are lanceolate to elliptical with rounded or slightly drawn-out apices, 5-17 μm long and 3-6 μm wide. The rapheless valve has a linear-lanceolate axial area that slightly widens in the middle. The asymmetrical central area on rapheless valve contains a hood on the internal valve surface.


Planothidium haynaldii

Planothidium lanceolatum var. haynaldii
Achnanthes lanceolata var. haynaldii

  1. Valves lanceolate to elliptical-lanceolate with capitate to subrostrate apices
  2. Valves 4.8-7.0 μm wide
  3. Rapheless valve with asymmetrical central area containing rimmed depression

Monoraphid - Valves are lanceolate to elliptical-lanceolate with capitate apices, 9-25 μm long, 4.8-7.0 μm wide. Small specimens have subrostrate, rather than capitate apices. The asymmetrical central area on the rapheless valve contains a rimmed depression on the internal valve surface. The striae are multiseriate, radiate throughout both valves, 14-15 in 10 μm.


Planothidium holstii

  1. Valves relatively large
  2. Apices slightly rostrate
  3. Central area "bow tie" to oval on raphe valve
  4. Central area large, broad on rapheless valve

Monoraphid - Valves are relatively large with slightly rostrate apices. The raphe valve has a distinct central area that is “bow tie” shaped. The rapheless valve has a large, broad central area, becoming more narrow toward the apices. Distal raphe ends are deflected to opposite sides of the valve.


Planothidium lanceolatum

Achnanthes lanceolata

  1. Valves lanceolate to elliptical-lanceolate with slightly drawn-out apices
  2. Valves 4.5-8.0 μm wide
  3. Rapheless valve with asymmetrical central area containing depression

Monoraphid - Valves are lanceolate to elliptical-lanceolate with slightly drawn-out apices, 7-24 μm long, 4.5-8.0 μm wide. The asymmetrical central area on rapheless valve contains a rimmed depression on the internal valve surface. The striae are multiseriate, radiate throughout both valves, 12-15 in 10 μm.


Planothidium rostratum

Achnanthes lanceolata subsp. rostrata

  1. Valves linear-elliptical with rostrate, subrostrate or narrowly subcapitate apices
  2. Valves 5.0-6.0 μm wide
  3. Rapheless valve with a hood
  4. Axial area on rapheless valve from narrow linear to expanded in the center

Monoraphid - Valves are elliptical with rostrate, subrostrate or narrowly subcapitate apices, 11.0-17.5 μm long, 5.0-6.0 μm wide. Rapheless valve has a linear axial area, which in some population considerably widens in the center. The central area on the rapheless valve is asymmetrical and contains a hood. The striae are multiseriate and radiate throughout both valves, 11-13 in 10 μm.


Platessa bahlsii

  1. Valves elliptic
  2. Central area on raphe valve very small
  3. Striae multiseriate
  4. Terminal raphe fissures absent

Monoraphid - Valves are elliptic. Raphe valve has a narrow linear axial area and a small central area. Raphe is filiform, straight, with slightly expanded distal and proximal ends. Rapheless valve has a linear–lanceolate axial area. Striae are multiseriate, radiate.


Platessa conspicua

Planothidium conspicuum

  1. Valves linear-elliptical
  2. Raphe valve with transversely rectangular central area reaching valve margins
  3. Striae biseriate
  4. Terminal raphe fissures absent

Monoraphid - Valves are linear-elliptical. The raphe valve has a narrow axial area and transversely rectangular central area that reaches valve margins. The rapheless valve has a lanceolate axial area and no distinct central area or the two middle striae may be slightly more distant from each other than other striae. The raphe is straight, with slightly expanded terminal and central ends, without terminal raphe fissures. Striae are almost parallel in the valve center, but become strongly radiate through both valves, biseriate, 12-16 in 10 µm.


Platessa hustedtii

Achnanthes hustedtii

  1. Valves elliptical
  2. Axial area on raphe valve narrow
  3. Central area on raphe valve transversely elliptical or rectangular
  4. Rapheless valve with wide lanceolate axial area
  5. Stria density 15-18 in 10 µ on both valves

Monoraphid - Valves are elliptical. The raphe valve has a narrow axial area and a transversely elliptical or rectangular central area. The rapheless valve has a wide lanceolate axial area and lacks a distinct central area.


Platessa kingstonii

  1. Valves elliptic
  2. Raphe valve with uniseriate striae
  3. Rapheless valve with triseriate striae
  4. Raphe valve central area transversely rectangular
  5. Rapheless valve axial area wide, elliptic–lanceolate

Monoraphid - Valves are elliptic. Raphe valve has a narrow linear axial area and transversely rectangular central area. Raphe is filiform, straight with slightly expanded external distal and proximal ends. Striae are uniseriate and moderately radiate on the raphe valve (26-30 in 10 μm). The rapheless valve has a wide elliptic–lanceolate axial area and short triseriate striae (12-15 in 10 μm).


Platessa lutheri

  1. Valves elliptic
  2. Striae on raphe valve uniseriate, 25-29 in 10 μm
  3. Striae on rapheless valve biseriate, 12-15 in 10 μm
  4. Central area on raphe valve bow-tie-shaped
  5. Axial area on rapheless valve wide, elliptic-lanceolate

Monoraphid - Valves are elliptic. The raphe valve has a narrow linear axial area and a wide, bow-tie-shaped central area. The striae on the raphe valve are uniseriate and strongly radiate. The rapheless valve has a wide lanceolate axial area bordered by short and broad biseriate striae.


Platessa stewartii

Planothidium stewartii

  1. Valves elliptic
  2. Axial area narrow
  3. Central area on raphe valve transversely rectangular
  4. Central area on rapheless valve small, often asymmetric
  5. Stria density 14-18 in 10 µm

Monoraphid - Valves are elliptic. Both valves have a linear axial area. The central area on the raphe valve is transapically rectangular, often reaching valve margins. The central area on the rapheless valve is small and often asymmetric. Striae are radiate and biseriate. The stria density on both valves is 14-18 in 10 µm.


Playaensis circumfimbria

  1. Longitudinal ribs present
  2. Valves panduriform, with slightly gibbous central margin
  3. Central area circular

Symmetrical biraphid - Playaensis circumfimbria has small panduriform valves with a slightly gibbous central margin. The apices are apiculate. The central area is relatively large and circular. Distinct longitudinal ribs are present.


Pleurosira laevis

Cerataulus laevis

  1. Ocelli 2
  2. Rimoportulae 2-3

Centric - Valves circular to elliptical and 65–120 μm in diameter. Two ocelli positioned opposite one another. Two to three rimoportulae are present, each with a small hyaline area surrounding each. Spinules are present across valve face and at the margin.


Psammothidium bioretii

Achnanthes biorettii

  1. Valves elliptical
  2. Central area on both valves transversely elliptical or rectangular
  3. Axial areas and raphes oblique to the apical axis, not parallel between valves, sigmoid toward apices

Monoraphid - Valves are elliptical. Both valves have narrow axial areas, which are often oblique to the apical axis, not parallel between the two valves, and sigmoid toward the apices. The central area is transversely elliptical or rectangular. The striae are radiate throughout .


Psammothidium chlidanos

  1. Valves linear-elliptical, often slightly gibbous at midvalve
  2. Both valves with linear axial area
  3. Both valves with transversely rectangular central area
  4. Raphe straight, without terminal raphe fissures

Monoraphid - Valves are linear-elliptical, often slightly gibbous at midvalve. Both valves have a linear axial area and transversely rectangular central area. The raphe is straight, without terminal raphe fissures. Striae are radiate on both valves, 27-33 in 10 µm, interrupted at the valve margin.


Psammothidium curtissimum

  1. Valves elliptical to linear-elliptical
  2. Central areas on both valves small
  3. Striae radiate

Monoraphid - Valves are elliptical to linear-elliptical. Valves very small, less than 10 μm in length. Both valves have small transversely elongated central areas. The raphe is straight, without terminal fissures. Striae are radiate on both valves, 27-31 in 10 µm.


Psammothidium daonense

Psammothidium grischunum f. daonensis

  1. Valves elliptical to linear-elliptical
  2. Central area on rapheless valve rhomboid with irregular edges
  3. Raphe straight

Monoraphid - Valves are elliptical to linear-elliptical. The raphe valve has a linear axial area, which widens into a transapically elliptical, rectangular, or diamond-shaped central area. The raphe is straight without terminal raphe fissures. The rapheless valve has a large rhomboid axial area with an irregular border. The striae are radiate, 24-30 in 10 µm.


Psammothidium didymum

  1. Valves small, less than 10 µm in length
  2. Valve outline linear-elliptical
  3. Central margin of valve constricted

Monoraphid - Valves are linear-elliptical, slightly constricted in the middle. The raphe valve has a small circular or elliptical central area. The raphe is straight, without terminal fissures. The rapheless valve has a large rhomboid axial area. Striae are radiate on both valves and interrupted at the valve margin. Striae number 28-32 in 10 µm on raphe valve, 25-28 in 10 µm on rapheless valve .


Psammothidium harveyi

  1. Valves elliptic-lanceolate, with rostrate apices
  2. Central area large, asymmetric on both valves
  3. Striae 22-25 in 10 μm
  4. Terminal raphe fissures curved to opposite sides

Monoraphid - Valves are lanceolate with rostrate apices. Both valves have narrow linear axial areas and large asymmetric central areas, often reaching one or both valve margins. The raphe is straight and the short terminal fissures curve to opposite sides.


Psammothidium helveticum

  1. Valves linear-elliptical
  2. Raphe with long terminal fissures curved to opposite sides
  3. Rapheless valve with large rounded, hexagonal or diamond-shaped central area

Monoraphid - Valves are linear-elliptical. The raphe valve has a bow tie-shaped central area. The raphe has long terminal raphe fissures curved to opposite sides of the valve. The rapheless valve has a large rounded, hexagonal or diamond-shaped central area. Striae are radiate on both valves, 24-30 in 10 µm.


Psammothidium lauenburgianum

  1. Valves are elliptic to elliptic-lanceolate
  2. Raphe straight
  3. Central area on raphe valve transversely rectangular to bow-tie shaped, symmetric or slightly asymmetric
  4. Central area on rapheless valve asymmetric, containing rimmed depression

Monoraphid - Valves are elliptic to elliptic-lanceolate. The raphe valve has linear axial area and transversely rectangular to bow-tie shaped central area, which is slightly asymmetric or symmetric. The rapheless valve has a lanceolate axial area and a large, transverse, asymmetric central area with a rimmed depression on the internal valve surface. The striae are radiate on both valves.


Psammothidium levanderi

  1. Valves elliptic to linear-elliptic
  2. Raphe valve with small, asymmetric central area
  3. Rapheless valve with rhomboid axial area

Monoraphid - Valves are elliptical to linear-elliptic. The raphe valve has a linear axial area and a small asymmetric central area. The rapheless valve has a rhomboid axial area, which often has an irregular border. The central area on rapheless valve is usually not differentiated from the axial area. Striae are slightly radiate in the center and strongly radiate at the apices of both valves, 25-31 in 10 µm. Areolae are often visible in LM.


Psammothidium marginulatum

  1. Valves elliptical-lanceolate to linear-elliptical
  2. Raphe valve with transversely elliptical central area
  3. Rapheless valve with wide rhomboid-lanceolate axial area

Monoraphid - Valves are elliptical-lanceolate to linear-elliptical. The raphe valve has a linear axial area, which widens toward the center of the valve, and a transversely elliptical central area. The raphe is straight, without terminal fissures. The rapheless valve has a wide rhomboid-lanceolate axial area. Striae are radiate on both valves, 23-27 in 10 µm.


Psammothidium pennsylvanicum

  1. Valves small, elliptic
  2. Striae 25-29 in 10 μm
  3. Areolae 35-40 in 10 μm
  4. Rapheless valve with strongly asymmetric central area

Monoraphid - Valves are elliptic. The raphe valve has a narrow linear axial area and transversely rectangular, or elliptic central area. The raphe is straight. The rapheless valve has a narrow linear axial area and an asymmetric central area. Areolae number 35–40 in 10 μm within each stria.


Psammothidium scoticum

  1. Valves linear-elliptical
  2. Rapheless valve with rhomoid axial area
  3. Striae radiate, 27-30 in 10 µm.

Monoraphid - Valves are linear-elliptical. The raphe valve has a linear to linear-lanceolate axial area, which widens toward the center of the valve, and a transversely elliptical to rectangular central area. The raphe is straight, without terminal fissures. The rapheless valve has a rhomoid axial area, which often sharply widens in the valve center. Striae are radiate on both valves, 27-30 in 10 µm.


Psammothidium semiapertum

Achnanthes hintzii

  1. Valves elliptic
  2. Striae 22-24 in 10 µm
  3. Areolae 25 in 10 µm
  4. Rapheless valve may have asymmetric central area

Monoraphid - Valves are elliptic. Both valves have narrow linear axial areas and transversely rectangular central areas. The central area on the rapheless valve may be asymmetric. The raphe is filiform and straight. There are 25 areolae in 10 μm along the stria.


Psammothidium subatomoides

Achnanthes subatomoides
Achnanthidium subatomoides

  1. Valves small and elliptical
  2. Raphe valve with a 'bow tie-shaped' central area
  3. Striae radiate

Monoraphid - Valves are very small and elliptical, with radiate striae. The raphe valve has a ‘bow-tie-shaped’ central area.


Pseudofallacia tenera

Fallacia tenera

  1. Valves linear-elliptical to broadly rounded
  2. Valves 6-11 µm long
  3. Striae composed of distinct areolae
  4. Small lyre-shaped hyaline area present

Symmetrical biraphid - Valves linear-elliptical to broadly rounded, ends not produced. Striae are composed of distinct puncta. A small lyre-shaped hyaline area is found on either side of the axial area.


Pseudostaurosira americana

  1. Valves linear to elliptic
  2. Sternum narrow and linear
  3. Striae slightly alternate
  4. Spines aligned with striae

Araphid - Valves are linear in large specimens, to nearly oval in smaller ones. The sternum is centrally placed and very narrow. Striae are punctate, uniseriate and slightly alternate (referring to how striae from opposite margins “meet” at the central sternum). Each spine is aligned with a stria.


Pseudostaurosira brevistriata

  1. Valves lanceolate to elliptical
  2. Axial area broad and lanceolate
  3. Striae near valve mantle
  4. Spines solid and spathulate

Araphid - Valves at the larger end of the size spectrum of P. brevistriata are lanceolate with rostrate ends. Smaller specimens are elliptical with rounded ends. The axial area is broad and lanceolate. Striae restricted to the valve margin. Striae are distinct, composed of wide, round to oval areolae. Spines are positioned on the valve mantle, in line with the striae. The spines are solid and spatulate.


Pseudostaurosira elliptica

Staurosira elliptica

  1. Valves elliptic to lanceolate
  2. Valve ends cuneate to narrowly rounded
  3. Striae short
  4. Apical pore fields reduced

Araphid - PSEUDOSTAUROSIRA ELLIPTICA HAS NOT BEEN VERIFIED IN NORTH AMERICA Valves of P. elliptica are elliptical to lanceolate with cuneate to rounded ends. Striae are short and usually composed of one round areola on the valve face and another on the valve mantle.


Pseudostaurosira neoelliptica

  1. Valves elliptical to linear
  2. Striae narrower than costae
  3. Areolae round
  4. Spines hollow

Araphid - Valves are lanceolate to elliptic, with broadly rounded ends to linear with subrostrate, rounded ends. Striae are narrower than the costae and formed by round areolae. Areolae decrease in size from valve face edge toward axial area. Spines are hollow, spatulate and positioned on the striae. Two distinct pore fields are present at each apex.


Pseudostaurosira parasitica

Fragilaria parasitica
Synedra parasitica
Synedrella parasitica

  1. Valves lanceolate
  2. Axial area broad and lanceolate
  3. Striae short
  4. Spines absent
  5. Apical pore fields recessed

Araphid - Frustules are lanceolate with rostrate to subcapitate ends. Axial area broadly lanceolate. The striae are short, restricted to the valve margins. Apical pore fields are present at both apicies and are well developed. Under the SEM, the pore fields can be observed to be recessed below the valve surface.


Pseudostaurosira pseudoconstruens

  1. Valve shape cruciform
  2. Round to transapically elliptical areolae
  3. Spines aligned with striae
  4. Striae usually restricted to valve margin

Araphid - Valves are cruciform with round sub-capitate to rostrate apices. The axial area is variable and may be wide to somewhat narrow. Striae are short and weakly radiate to very short and parallel at the apices. Areolae are round to elliptical on the transapical axis and easily distinguishable. Spines are aligned with striae.


Pseudostaurosira trainorii

  1. Valves round to slightly elliptical
  2. Axial area lanceolate to linear
  3. Spines solid
  4. Spines aligned with striae

Araphid - Valves are round to slightly elliptical. The axial area is typically lanceolate, but linear in some specimens. Some specimens may possess a broader axial area, but striae are never restricted to the valve margin. Spines are solid and positioned in line with striae. This taxon is difficult to recognize under the light microscope and identification may not be positive without scanning electron microscopy.


Punctastriata mimetica

  1. Valves variable
  2. Striae formed of net-like areolae
  3. Spines positioned on costae

Araphid - Valves are variable in shape - cruciform, rhomboid, lanceolate to oval. Striae are formed by net-like areolae. Spines are present, solid and positioned on a costa.


Puncticulata praetermissa

  1. Valve face nearly flat
  2. Central area with many uniform-sized areolae
  3. Central areolae scattered or arranged in weakly radiate rows
  4. Marginal striae short, with shadow lines

Centric - Cyclotella praetermissa has nearly flat valves and a central area consisting of many uniform-sized areolae. The central areolae are scattered or arranged in weakly radiate rows. Marginal striae are short and have shadow lines.


Puncticulata radiosa

Cyclotella radiosa

  1. Central areolae in radial rows
  2. Central areolae coarse
  3. Marginal striae occupy about half valve diameter
  4. Marginal striae with shadow lines

Centric - Cyclotella radiosa has a concentrically undulate valve face. The valve face is radially wrinkled. The central areolae are coarse, equal in size and arranged in radial rows. Marginal striae have shadow lines and occupy about half of the valve diameter.