Pennate diatoms with a raphe system on both valves of the frustule are biraphid. For example, Amphora, Epithemia, Gomphonema, Navicula and Mastogloia are all biraphid genera. In contrast, some pennate diatoms lack a raphe completely (i.e., Diatoma), while others have a raphe system on only one valve (monoraphid), such as Planothidium.
Barber, H.G. and Hayworth, E.Y. (1981). Guide to the Morphology of the Diatom Frustule. Freshwater Biological Association, 112 pp.