22 DESCRIPTION OF 
The shell of the dicarinata is quite light-coloured beneath, and rather a dark horn co- 
lour above, the change of colour taking place a short distance above the periphery of the 
whorl, between which and the superior carina it is quite dark. The superior carina is 
large and erect, the inferior one is smaller. All the whorls are visible beneath. Very mi- 
nute longitudinal strie cover the whole surface. 
Having several living specimens of both these species, I observed them closely with 
a lens while under water in a glass vessel. On the 15th of May, while I had a ¢ricarina- 
ta at the focus of my lens, I observed a small apple green, globose object, passing from un- 
der 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 moveable branchie, until entirely discharged against the per- 
pendicular side of the vessel in which it was kept, and there the mass remained attached, 
the parent having abandoned itimmediately. 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 
about four-twentieths of an inch. In other cases, I found the number of ova to differ; 
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 colour. 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 had the power 
of swimming, inverted from the surface of the water, like the Planorbes, Physa, &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 tricarinata requires from 
fourteen to fifteen days to be perfected in the ovum, from the time it is ejected and aban- 
doned by its parent. The dicarinata, I have no doubt, requires the same time. Numerous 
globules were deposited about the glass, which globules appeared all to resemble each other, 
and nearly all the individuals were of the species dicarinata. 
PALUDINA ANGULATA. 
Test inflata, tenui, fuscd, superné subvaricosd, inferné transvers? et minute striatd, minute perforata ; spird bre. 
viusculd, ad apicem tenebrosd; suturis impressis; anfractibus quinis, in medio angulatis; apertura magnd, subtrian. 
gulatd, intus subrubiginosd. 
Shell inflated, thin, brown, above somewhat varicose, below transversely and minutely striate, minutely perforate; spire 
rather short, dark at the apex; sutures impressed; whorls five, angular in the middle; aperture large, subtriangular, within 
subrubiginous. 
ee 
