Striae angled or curved toward the central nodule are called 'radiate' striae. Striae may be radiate in a specific part of the diatom valve. For example, the striae may be radiate throughout the valve, radiate only at the center valve, radiate only at the ends, etc.
Barber, H.G. and Hayworth, E.Y. (1981). Guide to the Morphology of the Diatom Frustule. Freshwater Biological Association, 112 pp.