158 MOLLUSCA. 
this naturalist had been deceived by some of the parisitical 
leeches which infest the aquatic pulmonifera, and that, instead 
ot breathing by means of tubular gills, the animal of the Z. 
auricularia possesses, like those which it resembles in other 
characters, a pulmonary cavity. 
Genus Puysa.—Pillar-lip destitute of a fold, and the 
whorls are sinistral. (Zool. Journ. vii. 363.) The external ap- 
pearance of the animal issimilar to the Limnea; but the mar- 
gin of the cloak is loose, divided into lobes, and capable of 
being reflected over the surface of the shell near the mouth. 
This genus was instituted by Draparnaud. The Bulla fonti- 
nalis of British authors is regarded as the type of the genus. 
Genus ApLEexA.—Pillar-lip, with a fold. This genus 
was instituted by us for the reception of the Bulla hypnorum 
and rivalis of British writers. The shell is more produced 
than in the Physa. The cloak of the animal is incapable of 
being reflected on the shell, and its margin is destitute of lobes. 
Genus PLANnorpis.—Cavity of the shell entire. This is 
another sinistral genus; the vent, pulmonary cavity, and 
sexual organs, being on the left, and the heart on the right 
side. The P. corneus, the type of the genus, pours forth, 
when irritated, a purple fluid from the sides, between the foot 
and the margin of the cloak. 
GENUS SEGMENTINA.—Cavity of the shell divided. Ex- 
ternally, the shell appears similar to Planorbis; but inter- 
nally, it is divided by testaceous, transverse partitions, into 
several chambers, which communicate with each other by 
triradiated apertures. It is uncertain whether the animal 
is to be considered as dextral or sinistral. This genus was 
instituted by us several years ago, for the reception of the 
Nautilus lucustris of Lightfoot, first described and figured in 
Phil. Trans. vol. \xxvi. p. 160. tab. 1. f..1, 8. 
