416 



MOLLUSCA : GASTEROPODA. 



FIG. 601. 



FIG. G03. 



I'laniirbis lent us. Say. 

 United States. 



Lim-nn-a desiiJiusa, Say. 

 United States. 



ftiysn hetcmstropha, Say. 

 United States. 



FIG. 601. 



FIG. 605. 



FIG. COT. 



Helicina orbiculala, Say. 

 United States. 



FIG. 606. 



Acicula fused 

 Britaiu. 



Cyclostoma dfntn/um. 



United States. 



Tornatrlla tnrnatilis. 

 Britain. 



Some of the families of the Pnlmonifera are provided 

 M'ith an operculuzn. Tliese are the Cyclostomidse (Cydo- 

 stoma, HeUcina, etc., Figs. 005, CUi), and the Acieulidae 

 (Acicula, etc., Fig. 60G). 



3. The OpiSTiioBEANcniATA are gasteropods whose gills 

 are more or less branched or fasciculated, and placed 

 towards the hind part of the body. The sexes are united 

 in each individual. In most cases the shell is only rudi- 

 mentary, or wholly wanting; but some kinds, as Torno- 

 tella, etc. (Fig. 607), have the shell as well developed as 



FIG. 608. 



FIG. fi09. 



FIG. 610. 



Atlanta Pfrnnii. 

 South Atlantic. 



Bulln solitaria. Say. 

 United States. 



Elysia viridis, Mont. 

 Britain. 



