380 Mr. Jeffreys on the Testaceous Pneumonohranchous 



a. major, ventricosior, albida. 

 /3. ovalis, fulva ; spirA prominul^. 



Bulla rivalis. Maton Sf Rackett in Linn. Trans. 8. 

 p. 126. t.4^.f.2. 

 y. oblongiuscula, fragilissima, resiliens ; apertura oblong^, 

 angustiore. 

 Planorbis gelatinus. Mull. Verm. 2. p. 170? 

 5. minor, globosa. 



Bulla fluviatilis. Turton's Coiich. Diet. 



On aquatic plants in slowly-running streams. 



The variety j8., 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 

 a larger 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 it in a small stream on Monavallach mountain 

 near Kilmacthomas, Waterford. 



The animal is phytophagous, feeding principally on 

 water-cresses and other aquatics. The spawn is cast in the 

 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, 

 its form alters to oblong, and the embryos are very distinctly 

 seen, in number from three to ten, inclosed in its gelatinous 

 and now transparent covering. In about a month or five 



weeks. 



