MOLLUSCS, VERMES AND HYDROZOA 



occurs from Maine to Pennsylvania and Ohio, and is very numerous on 

 the muddy shores of the Delaware and Schuylkill rivers. 



A. granum is a very small species, not much larger than a pin's head, 

 found in ponds near Philadelphia. It has a slender, conic-ovate yellowish- 

 brown shell, having four or five convex whorls, deeply impressed suture 

 and orbicular aperture. It ranges from Lake Superior to Virginia. 

 Gould mentions another species, A. pallida, which has not been described 

 as occurring in the Middle States. 



BiTHYNiA. These small whorled snails are usually found in ponds, 

 ditches, canals and slow streams of not too cold water. They are oviparous 

 and water-breathing, differing principally from some of the smaller Physa 

 in having the whorl of the shell dextral. They thrive fairly well in the 

 aquarium but are vegetable feeding and indifferent scavengers. 



B. tentaculata. Fig. 157, has a glossy grey or horn-colored conical y^ to 

 Yi inch long shell of six rounded whorls, with a distinct suture and pointed 



apex. The body whorl 



I 



takes up more than half 

 the length of the shell. 

 The body is almost black, 

 spotted with yellow and the 

 divergent filiform tentacles 

 are long and slender. The 



BUhynta ttnlaculata. Enlarged. CyCS are black and Set at thc 



base of the tentacles and the obovate operculum calcarious and brittle. It 

 is a harmless oviparous snail, feeding principally on decaying vegetation. 

 Found quite generally in the Eastern and Middle States. 



Melaniid^. It should be noted of this family that it contains many 

 genera and hundreds of species. Almost every river drainage system of 

 the world has either distinct or closely allied forms; those of the United 

 States being the Strepomatidae, of which there are many local genera, the 

 most compion of the Eastern and Middle States being the Goniobases and 

 Anculosa of the Hudson, Susquehanna, Delaware and Potomac basins. 

 For brevity these only are described, the others are closely related similar 

 forms. 



GoNioBAsis. This genus has most beautiful conical or fusiform 

 shells, showing faint lines of growth and often series of longitudinal ridges 

 on the seven to ten whorls. Occurs quite generally in flowing waters. 



G. virginica, Fig. 1 58, is a very common species of the middle Atlantic 

 coast States. It has a truncated turreted yellowish-brown % to i inch long 

 shell, usually eroded at the spire. The eight to ten whorls are marked 

 with a dull reddish line near the base of the whorls, with a second line 



228 



