488 



MOLLUSKS : GASTEROPODS. 



Fig. 439 TORNATELLID^:. This Family compris- 



es gasteropods which have the shell solid, 

 aperture long and narrow, and columella 

 plaited. There are fifty living and one 

 hundred and fifty fossil species. 



BULLID.E. This Family contains one 

 hundred and fifty living and nearly one 

 hundred fossil species. They have the 

 shell globular or cylindrical, convoluted 

 and thin. Marine. 



DORID.E, TRITONID^:, ALOL.IDJE, ELY- 

 SIAD,E, &c. These Families contain sea- 

 slugs which have no shell except in the embryo state. 

 Three hundred species. Figs. 441 -444. 



Tornatella tornatilis, 

 L. Britain. 



Fig. 440. 



Bulla solitaria, Say. 

 United States. 



Fig- 443- 



Fig. 442. 



Doris Johnstoni, Alder & Hancock. 

 Britain. 



Fig, 444. 



Elysia "viridis, Mont. 

 Britain. 



Eolh coronata, Forbes. 

 Britain. 



Tritonia plebeia, 

 Johnston. Britain. 



Figs. 445, 446 



SUB-SECTION II. 



THE ORDER OF HETEROPODA, OR HETEROPODS. 



THIS Order comprises mollusks whose 

 general appearance differs considerably 

 from the true gasteropods. They live in 

 the open sea, and swim at the surface. 

 ii, LeS. They belong to two families, Firolidse 



South Atlantic. i A i ^ i 



and Atlantidae. 



