PHYSA. 



49 



tliat since the year 1869 (when the mollusc was 

 found in small quantity) it had increased its area of 

 distribution and multiplied so much as to be likely to 

 become one of the commonest of our local shells." 



GENUS IL—PHY'SA* LAMARCK. 



Body oblong, spiral ; tentacles long, rather slender ; foot 

 elongated, roundish-oval in front, pointed behind, attached to 

 the body by a broad, short pedicle ; jazu single, slightly arched. 



Shell oblong or oval, very thin, transparent ; spire more or 

 less produced, sinistral. 



This genus seems to form a connecting link between 

 Planorbis and Limricea, partaking of some of the cha- 

 racters of each, but differing from both in the form of 

 the shell, which is sinistral. The Physce inhabit clear 

 water ; they are gregarious and herbivorous. Their 

 eggs, which are oval and of a glassy texture, are 

 incased in gelatinous capsules or coverings, which are 

 cemented to stones and other substances under water. 

 There are only two species in Great Britain. 



A. Mantle simple, not covering the shell ; sJiell covered 

 with an epidermis ; spire long. 



I. PhYSA HYPNO'RUM,t LINN£. Pl. IV. 



Body dark grey or brown, sometimes slaty-black, of a texture 

 resembling velvet, covered with exceedingly small blackish 

 specks ; tefitacles long, slender, much pointed, grey more or less 

 deep in colour ; eyes somewhat indistinct, very small, black ; 

 foot oblong, lanceolate, narrow, and obtuse in front, ending 

 behind in an oval, depressed, and somewhat pointed tail, which 

 is of a paler colour than the rest of the body, and more distinctly 

 spotted with grey or black. 



Shell spindle-shaped, thin, semitransparent, very glossy, 



* A bladder. f Living in Hypnu7n^ one of the genera of mosses. 



E 



