10 



13. Sph. e m a r g i n a t u m, Prime. 



Cyclas emarginata, Prime, Bost. Proc. iv. 156, 1851. 



Animal not observed. 



Shell triangular, nearly equilateral, convex, tumid, anterior and posterior 

 margins abrupt, posterior slightly more distended, basal margin curved ; valves 

 soJid, interior white ; beaks very full, prominent, nearly central ; ligament 

 distinct ; sulcations regular, not heavy ; epidermis brown, with several nar- 

 row transverse zones of a dark color at regular intervals ; hinge margin 

 curved ; cardinal teeth single, quite distinct ; lateral teeth not much elongated, 

 strong. 



Long. 6-16 ; lat. 6-16; diam. 4-16 inches. 



Hab. N. America, in the region of Lake Superior. 



(Cabinet. Agassiz and Prime.) 



The triangular and very tumid form of this species is quite singular ; it 

 differs from the Sph. Vermontanum in being more tumid, fuller, in having 

 larger beaks and in being much less broad at the base. The young shell is 

 more elongated and less tumid than the adult. A rare species. 



14. Sph. flavum, Prime. 



Cyclas flava, Prime, Bost. Proc., iv. 155, 1851. 



Animal not observed. 



Shell transversely rounded, compressed, equilateral, delicate, margins gene- 

 rally rounded, the posterior a little distended ; beaks central, not full, more 

 or less deputed ; valves very slight, interior whitish ; sulcations pretty deep, 

 regular ; epidermis light, of a greenish yellow color ; cardinal teeth small, 

 in the shape of the letter V reversed ; lateral teeth elongated. 



Long. 7-16 ; lat. 5-16 ; diam. 3-16 inches. 



Hab. N. America, at the Sault St. Marie, Lake Superior. 



(Cabinet. Agassiz, Jay and Prime.) 



This is a very slight and delicate species, quite distinct from any others but 

 the Sph. patella, to which it bears some general resemblance from its shape ; 

 it is, however, more compressed, less high, and the exterior of the valves is 

 very different, as they are nearly smooth in Dr. Gould's shell. Found not 

 unplentifully in the one locality. 



