Invertebrate Gallery of the Indian Museum. I2i 



covered with a dark epidermis, and are closed by a horny 

 operculum. 



17th Family, ValvatJciae [Case 147B]. 



The Valvatidx are a small family of pond-snails, 

 occurring chiefly in the temperate parts of the northern 

 hemisphere. The animal is remarkable — see the enlarged 

 drawing in Case 147B — in having its gill-comb exposed. 

 The shell, which is covered with epidermis, is a spiral, 

 usually coiled in a nearly horizontal plane, and is closed 

 by a horny operculum. 



i8th Family, Ampullaridse [Cases 147C— 148A]. 



These are pond and river snails found principally within 

 the tropics. Although the animal possesses a gill, it also 

 has a part of the mantle-cavity shut off to form a lung- 

 sack, so that it can live as well on dry land as it can 

 in freshwater. The shell is a short spiral covered with 

 dark epidermis and closed by an operculum which is some- 

 times stony. 



/5. GASTROPODA AZYGOBRANCHIA PNEUMOCHLAMYDA. 



[Cases jiE ;a, f , or]. 



In this sub-Order of crawling Gastropods the gill is 

 absent, and the mantle-edge is adherent to the body in the 

 greater part of its extent to form a lung-sack. The 

 species of this large group are all, like the true snails, 

 terrestrial, but they differ from the true snails in many 

 important details of internal organization and also in pos- 

 sessing an operculum to close the shell. This sub-Order 

 comprises the three families of the Cyclostomidw, Helici- 

 nidse^ and Aciculidx. 



y. GASTROPODA AZYGOBRANCHIA SIPHONOCHLAMYDA. 



[(Eases l48|5~X66f ]. 



In this sub-Order uf crawling Gastropods the edge of 



the shell is notched, or is drawn out to forma long narrow 



channel, for the passage of a corresponding process of 



the mantle. The animals are almost exclusively marine 



