104 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



tacles. Shell globose, whorls convex, apex usually rounded. Umbilicus small, 

 aperture rounded. Shows considerable variation. Shell may be conic, spire 

 elongated and apex sharp. The sutures vary in distinctness. Eggs laid in small 

 triangular capsules on weeds, sticks, stones and even on the shells of other 

 molluscs. (PI. X, Fig. 9). 



Amnicola emarginata, Say. Not numerous. Found with A. limosa. Dis- 

 tinguished from it by the truncated apex, the first whorl not rising above the 

 second. Spire also more elongated than usual in A. limosa. 



Amnicola lustrica, Say; not abundant. Occurs with other species of Amnicola; 

 dredged in 20 fathoms or more of water. Compared with A. limosa, shell thinner, 

 spire much more elevated, apex sharp, body whorl scarcely larger than the pre- 

 ceding one. (PI. X, Fig. 10). 



Family valvatidae. 



Two species belonging to one genus occur. 



Genus Valvata. 



Of the two species, one, V. tricarinata occurs abundantly. Operculate. The 

 plume-like gills borne within the mantle-cavity. 



Valvata tricarinata, Say., abundant in weedy places among islands on either 

 sandy or muddy bottoms. Occurs on sandy bottoms even to depth of 20 fath- 

 oms. Prominent carinae, usually three. Umbilicus broad, open to apex. Whorls 

 loosely appressed. Quite variable. One or all of the carinae may be lacking or 

 indistinct. The order of their reduction appears to be peripheral, lower, upper. 

 In sandy places malformations in which whorls do not touch preceding whorls 

 occur, seen in early whorls, body whorl or intermediate ones. Found in white- 

 fish stomachs. (PI. XI, Fig. 21). 



Valvata sincera, Say. Found only in dredgings in sandy places. Occurs 

 at depths of up to 20 fathoms. Not abundant. Compared with V. tricarinata 

 there are no carinae and whorls are more rounded. There are distinct, sharp, 

 elevated ridges, parallel to lines of growth. In the young these ridges are finer 

 and more closely placed. Subject in sandy places to malformations similar to 

 those occurring in V. tricarinata. Abundant in stomachs of whitefish, (PI. XI, 

 Fig. 22). 



Family viviparidae. 



Represented by one species belonging to Genus Campeloma. 



Genus Campeloma. 



Operculate. As family name indicates young are produced alive, 

 Campeloma decisum. Say; occurs abundantly in sheltered bays with soft 

 mud bottoms and in sand channels with decaying vegetable content. Congre- 



