228 UNITED states geological survey of the teeeitoeies. 



Fig. -jr.. 



Illustrations of the subgenus Cymella. 



Fig. 28. Fig. 29. 



« t .> j> fc 



Fig. 2f> 



Fig. 27 



Fig. 30. 

 Cymella Mia, Conrad. 



Fig. 25. Exterior of right valve, natural size. 



Fig. 26. Hinge-view of right valve, magnified two diameters, to give a general 

 view of its appearance and fin- comparison with iig. 21, of Liojrist ha 

 proper. 



Fig. 27. The same, of opposite valve, for comparison with fig. 22. 



Fig. 28. Dorsal view, magnified, to show profile or projection of hinge-teeth. 



Fig. 29. Hinge anil adjacent parts of right valve, more highly magnified, and turned over so as to lie 

 seen from inner side, to show details of teeth and pits ; a. t. being the anterior tooth ; a. p., the 

 anterior pit : p. t., the, posterior tooth ; p. p., the posterior pit ; and,/'., the fulcrum. 



Fig. 30. Same view of the left valve, magnified, and seen in same way ; the letters pointing to the corre- 

 sponding teeth and pits as in the other valve. 



Shell equivalve, inequilateral, transversely subovate, being usually 

 narrower, inure compressed, and often subrostrate behind, and ventricose in 

 the central and umbonal regions, nearly always extremely thin ; extremities 

 rounded in outline, the posterior side usually a little gaping; surface granular, 

 and varying, according to the sections and species, from radiately costate on 

 the flanks and front of the valves, to strongly undulate concentrically, with 

 only a few impressed, radiating lines on the middle, or rarely nearly smooth, 

 concentrically striate, or furrowed, with obsolescenl radiating striae; dorsal 

 margins generally inflected so as to form a sort of false area along its entire 

 length ; hinge with two prominent cardinal teeth, projecting out at right 



