BRlCHIOrODA. 



377 



on a low soi^tal ridge (s) ; dorsal valve with a in'ominent septum 

 (s) supporting a spoon-sliaped central process (u) ; oral lamcllra 

 long and slender (o). Foramen angular, cardinal process dis- 

 tinct (y). Fossil, 9 species. Garb.— Permian (Magnesian lime- 

 stone.) Germany and England. 



Fig. 177. luterual cast.* 



Fig. 178. Section. 



Pentameeus, Sowerby. 



Etymology, loentameres, o-partite. 



Synonym, Gypidia (concliydium), Dalman. 



Type, P. Kniglitii, PI. XV., Fig. 22. Fig. 179. 



Shell impunctate, ovate, vcntricose, with a large incurved 

 beak ; valves usually plaited ; foramen angular ; no area or 

 deltidium ; dental plates {d) converging, trough-like, supported 

 on a prominent septum (s) ; dorsal valve with two contiguous 



Longitudinal, 



Fig. 179. 



Transverse section. 



longitudinal septa [s s) opposed to ihc plates of the other 

 valve. 

 Oral lamellae have been detected by Mr, Salter in P. liratus ; 



* Ventral Bide of cast, showing tlie V-sliaped cavity of the dental plates, and the 

 Inipiesbicns of bianoliial veins, accompanied by arteries (after King), 



