VAIiVATA. 11 



apple green, globose object, passing from under the aperture of the shell. 

 This was shortly followed by others, and soon a transparent gelatinous 

 mass became visible. This mass was passed slowly over the right side 

 of the neck, under the pectiniform movable branchiae, until entirely dis- 

 charged against the perpendicular side of the vessel in which it was kept, 

 and there the mass remained attached, the parent having abandoned it 

 immediately. The time was fifteen minutes from the first appearance of 

 the mass until it was fairly discharged. The green globules were the ova, 

 of which I counted thirty in the transparent, globose gelatinous mass, which 

 was not more in diameter than one-twentieth of an inch, the transverse 

 diameter of the shell being aboiit four-twentieths of an inch. In other cases 

 I found the number of ova to ditfer ; some masses having only ten or twelve. 



On the 23d (eight days after), the ova were so far advanced as to be 

 changed to a dull faded green, the mass enveloping them having changed 

 by degrees in transparency, and becoming of a slightly ferruginous color. 

 As yet, no change of bulk or arrangement was observed. 



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 swimmino-, 

 inverted from the surface of the water, like the Planorbes, Physae, &c. Most 

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

 The action of the mouth 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 hicaritiata 

 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 bicarinata. (Lea.) 



Fig. 15. Valvata carinata, ^ovfB.,]. c, Fig. 16. 



is figured only ; no description is 

 given (fig. 15). 



Valvata untcarinata, CeKay. — Shell 

 F. carinata. small, apex depressed ; whirls 3 or 4, 

 impressed with minute incremental 

 strife, 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 ; Valvata unicarinata. 

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



