380 Mr. Jerrreys on the Testaceous Pneumonobranchous 
a. major, ventricosior, albida. 
B. ovalis, fulva; spirá prominula. 
Bulla rivalis. Maton § Rackett in Linn. Trans. 8. 
p. 126. t. 4. f. 2. 
y. oblongiuscula, fragilissima, resiliens ; apertura oblonga, 
angustiore. 
Planorbis gelatinus. Müll. Verm. 2. p. 170? 
6. minor, globosa. 
Bulla fluviatilis.  T'urton's Conch. Dict. 
On aquatic plants in slowly-running streams. 
The variety 8., which has I suspect been mistaken by the 
learned authors of the Catalogue of British Testacea for a 
distinct species, is of a paler colour, less fragile texture, and 
has the spire, which consists of from five to six volutions, 
more produced. Such I have received from Oxfordshire, of 
alarger size. In the Physa acuta of Draparnaud, specimens 
of which I have from one of the North American lakes, the 
spire is nearly exactly central; and, though not more pro- 
duced, tapers to an exceedingly fine point. ‘The aperture 
is also narrower and more elongated. The variety a. was 
favoured me by Mr. Dillwyn, who in company with Dr. 
. Leach found itin a small stream on Monazallach mountain 
near Kilmacthomas, Waterford. - 
The animal is phytophagousy fedes principally on 
water-cresses and other aquatics. The spawn is cast inthe ` 
beginning of April and following months, and at first ap- 
pears a globular and confused mass, of a clear white colour ; 
. but in process of time and before the young are excluded, 
| cM form alters to oblong, and the embryos are very distinctly 
, in number from three to ten, inclosed in its gelatinous 
and now transpar it covering. In about a month or five 
: : weeks, 
