Mollusca of Great Britain. | 381 
weeks, the young, with their testaceous coats completely 
formed, and about the size of a pin's head, burst their en- 
velope, and immediately enter upon their new functions, 
swimming and walking with great activity. 
2. Hypnorum. 
Animal nigrescens. Tentacula superné albida. Susten- 
taculum latum. 
Testa elongato-fusiformis, subventricosa, acuminata, fragilis, 
diaphana, polita, fulvo-cornea. Anfractus 7, valdé tur- 
rii. Apertura oblonga. 
Long. 0.5.— Diam. 0.2. 
Physa hypnorum. Drap. Hist. des Moll. p. 55. t. 3. 
f. 12, 13. 
Bulla hypnorum. Linn. Syst. Nat. 1. p. 1185. 
Planorbis turritus. Müll. Verm. 2. p. 169. 
In slowly-running streams in many parts of Great Bri- 
tain. Some specimens before me, from the garden ponds 
of Fremington-house, Devonshire, are of unusual size, 
measuring full three quarters of an inch in length. I have 
only found them in the hottest days of the summer and 
autumn months on the surface of the water, where they lie 
floating with their shells downwards. | 
Genus XV. Ee Müt. E 
| DE tentaculis filiformibus, acum [ ın an- 
Testa po r'apfacnbis € 'aceis : 
sertà : aperturá subrhomboideàá, ere indue | 
bus: peristomio simplici. 
