LAMELLIBRANCHIATA : VENERID^E. 



493 



- This Family contains acephala which 

 have the shell orbicular. There are one hundred and 

 twenty living, and three hundred and fifty fossil species. 

 Marine. Fig. 463. 



CYCLADID^E. - -This Family contains acephala which 

 have the shell sub-orbicular, with a thick horny epider- 

 mis. There are two hundred living, and one hundred 

 fossil species. Fresh water. Figs. 462, 464. 



Fig. 461. 



Fig. 464. 



Fig. 463. 



Fig. 462. 



Splierriitm rhom- Thyasira Gonldii, 

 boidcum, Say. Stim. Coast of 



Northern States. New England, sphecriwn 



Say. Northern States. 

 A starte castanca. Say. 

 Casco Bay and southward. 



CvpRiNiDyE. - - This Family comprises acephala which 

 have the shell oval or elongated, valves solid, and the 

 epidermis thick and dark. There are more than one 

 hundred living, and three hundred and fifty fossil species. 

 Marine. Fig. 461. 



VENERID.E. This Family embraces acephala which 

 have the shell sub-orbicular or oblong, and the hinge with 



Fig. 465. 



Fig 466. 



Mactra elliptica. Britain. 

 Cytherca dianc, L. Two thirds. 

 West Indies. 



three diverging teeth in each valve. There are nearly six 

 hundred living, and three hundred fossil species. Marine. 



