VALVATA. 



51 



On the 29th, (fourteen days after), the mass was observed to be opened, 

 and with a lens of considerable power I could plainly see a motion in most 

 of the ova, the rounded form of the shell being easily discerned within. 



On the 30th, (fifteen days after), most of the young shells had broken 

 their filmy bonds, only six or seven remaining : their motion was very 

 apparent, and their minute black eyes could be plainly seen. I observed 

 to-day, for the first time, that the Valvata has the power of swimming, 

 inverted from the surface of the water, like the Planorbes, Phi/sie, &c. Most 

 of the young were in that position, and could move comparatively fast. 

 The action of the moutli in the adult, when swimming in this way, was 

 constant, and changed from an oval to a circular form. 



From the above observations, we may conclude that the Valvata trica- 

 rinata requires from fourteen to fifteen days to be perfected in the ovum, 

 from the time it is ejected and abandoned by its parent. The hicarinata, 

 I have no. doubt, requires the same time. Numerous globules were depo- 

 sited about the glass, which globules appeared all to resemble each other, 

 and nearly all the individuals were of the species hicarinata. (Lea.) 



Fig. 86. Valvata carinafa, Sowb., 1. c, Fig. 87. 



is figured only ; no description is 

 given (fig. 86). 



Valvata unicarinata, DeKay, — Shell 



V. cartnata. small, apex depressed ; whirls 3 or 4, 

 impressed with minute incremental 

 striae, all flattened above and bounded by a revolving 

 rib or keel, which in the younger individuals ascends 

 to the summit : aperture circular, nearly vertical, 

 scarcely modified by the keel ; opercle corneous, thin, 

 with concentric striae ; umbilicus wide, profound, ex- 

 hibiting all the volutions ; color milky bluish- white ; 

 apex often tinged with rufous. Height .1, diam. .15. 



These dimensions are from one of the largest size, obtained from Lake 

 Champlain, where they are very abundant, and from the Erie Canal. It is 

 allied to the preceding ( V. tricarinata), and forms the passage to V. sincera. 

 Some eminent conchologists suppose this, and perhaps the following ( V. 

 sincera) to be mere varieties of V. tricarinata. It approaches the V. hume- 

 ralis, Say, from Mexico ; but it is smaller, not so much depressed, and has 

 a wider umbilicus. {DeKay.) 



I have evidence of its ranging at least from New England and 

 Pennsylvania to Council Bluff and Methy Lake, lat. 5Y°. 



Haldeman says the ova are deposited from the first day of 

 March to the end of July, in transparent masses half a line in 

 diameter, each containing a number of germs of a bright green 

 color dotted with yellow. 



Valvata, unicarinata. 



