BEACHIOrODA. 



377 



on a low septal ridge (s) ; dorsal valve with a prominent septum 

 (s) supporting a spoon-shaped central process {v) ; oral lamellae 

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

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

 stone.) Germany and England. 



Fig. 177. laternal cast,* 



Fig. 178. Section. 



Pentamerijs, Sowerby. 



Etymology, pentameres, o-partite. 



Synonym, Gypidia (conchydium), Dalman. 



Type, P. Knigktii, PI. XY., Pig. 22. Pig. 179. 



Shell impunctate, ovate, ventricose, 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 the plates of the other 

 valve. 



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



* Ventral side of cast, showing the V-shaped cavity of the dental plates, and the 

 impressions of branchial veins, accompanied by arteries (after King), 



