Planorbis. MOLLUSCA. PULMONIFERA. 2T7 



118. A. rivalis. — Spire short, pointed ; aperture contracted 

 anteaily. 



Bulla riv. Maton and Rackett, Linn. Trans, viii. 126. tab. iv. f. 2. Turt' 

 Conch. Diet. 26. — Physa subopaca, Lamark, Hist. Vert. vol. vi. p. 2. 157- 

 —In slow streams, rare. 



Length scarcely half an inch ; pale horn-coloured, glossy; whorls five, the 

 last occupying f ths of the whole length ; apex pointed ; aperture with the 

 outer-lip more rounded than the last, and the pillar-lip more recurved an- 

 teaily. — This shell was first recorded as having been found in Hampshire, by 

 Mr Hay. Dr Turton has seen it alive at Naas, in Ireland. Other localities 

 have been mentioned, but they are regarded as spurious.— -It is a common 

 shell from the West Indies. 



Gen. XXXII. PLANORBIS— Cavity of the sheU entire, 

 sinistral ; the vent, pulmonary cavity, and sexual organs on 

 the left side ; tentacula fihform. 



* Whorls rounded on the margin. 



119- P- corneus. — Whorls four, rounded; concave above; 

 mouth suborbicular. 



Cochlea pulla. List. An. Ang. 143. Conch, t. 137- £ 41 — Planorbis 

 purpura, MulL Verm. ii. 154. — Helix cornea, I.inn. Syst. i. 1243. 

 Penn. Brit. Zool. iv. 134. Mont. Test. Brit. 449 — In ponds and slow 

 streams. England. 

 Breadth about an inch ; brown, glossy ; lines of growth distinct ; whorls 

 above, increasing rapidly, and forming a central cavity ; below, the whorls are 

 nearly on the same plane, well defined by the separating line ; last whorl pro- 

 jecting into the cavity of the aperture. When in-itated, the animal pours 

 forth a purple fluid from the sides, between the foot and margin of the cloak. 

 The H. nana of Pennant is the young of this species. 



120. P. spirorbis. — Whorls five, rounded ; flat above ; aper- 

 ture suborbicular. 



Mull. Verm, ii. 161. H. spin Linn. Syst. i. 1244. Mont. Test. Brit. 

 455, Suppl. tab. xxv, f. 2, — In pools. 

 Breadth about /gths of an inch ; nearly equally flat on both sides ; of a 

 brown colour; whorls round, slender, and increasing in size very gradually ; 

 deeply divided by the separating line ; aperture nearly round, scarcely inter- 

 rupted by the body-whorl.— This species is stated by Montagu as common in 

 England. In Scotland it has occurred to us only in Livingstone Woods, 

 West Lothian. 



121. P. contortus. — Whorls six, compressed ; flat above, con- 

 cave below. 



Helix con. Linn. Syst. i. 1244 Plan. con. Mull. Verm. ii. 162. — H. con. 



Mont. Test. Brit. 457. tab. xxv. f. 6. — In pools and ditches, not com- 

 mon. 



Breadth about /jths of an inch ; whorls compressed, rounded, even on the 

 upper side, narrow, and deeply divided by the separating line ; beneath, a 

 large central cavity ; aperture narrow, bent. 



