LAMELLIBRANCHIATA I VENERID.E. 



493 



LUCINID.E. 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. 462. Fig. 463. 



Sph&rium rhont- 

 boideutn, Say. 

 Northern States. 



Thyasira Gouldii, 



Stim. Coast of 



New England. S p)utrium partumeium, 



Say. Northern States. 



A s tarte castanea, Say. 

 Casco Bay and southward. 



CYPRINID^:. 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. 



Cytkerea dionf, L. Two thirds. 

 West Indies. 



Mactra elliptica. Britain. 



three diverging teeth in each valve. There are nearly six 

 hundred living, and three hundred fossil species. Marine. 



