Segmentina. MOLLUSCA. PULMONIFERA. 279 



— 127. P. carinatus. — Whorls four ; keel near the middle of the 

 whorl, and entering the aperture. / 



Cochlea fusca, List. An. Ang. 145. Conch, t. 138. f. 42.— Helix Planor- 

 bis, Linn. Syst. i. 1242. — P. car. Mull. Verm. ii. 157-— H. car. Mont. 

 Test. Brit. 451. Supp. t. xxv. £ 1 — In ditches. 

 This shell chiefly differs from the preceding, in the whorls above increasing 

 more rapidly, forming a larger central cavity ; in the greater flatness below ; 

 in the ridge entering the aperture ; and in the tentacula being pellucid yel- 

 low. 



EXTINCT SPECIES. 



1. P. ajlindricus.— Cylindrical; left side concentrically striated ; volutions 

 three or four, adpressed ; aperture oblong, quadrangular. — Sower. Min. Conch, 

 t. 140. f. 2. — Fresh-water formation, Isle of Wight. 



2. P. obtusus. — Depressed ; left side most concave ; volutions embracing^ 

 slightly compressed on the right ; aperture obliquely and obtusely obcordate* 

 —Sower. Min. Conch, t. 140. f. 3. Isle of Wight. 



3. P. lens Lenticular, subcarinated ; volutions embracing ; aperture very 



oblique, obcordate Sower. Min. Conch, t. 140. f. 4. Isle of Wight. 



4. P. hemestoma Depressed, smooth ; right side convex, umbilicate ; left 



side flat; aperture oblique, sub triangular. — Soioer. Min. Conch, t. 140. f. C. 

 Plastic-clay, Plumstead. 



5. P. radiatus Lenticular, radiated ; left side umbilicate ; volutions near- 

 ly concealed ; aperture obcordate. — Sower. Min. Conch, t. 140. f. 5. Green- 

 sand, 



6. P. euomphalus.~— Depressed, subcarinated ; concentrically striated ; right 

 side flat; left side hvrgely umbilicate; aperture subtriangular. — Sower. Min. 

 Conch, t. 140. f. 1, 9. Isle of Wight — The P. rotundatus of Brongniart is 

 mentioned in the Mineral Conchology as occurring in Hordwell Cliff, along 

 with Limnea columellaris, t. 528. The three last species are probably marine, 

 and belong to the genus Skenea. 



Gen. XXXIII. SEGMENTING— Shell divided internally 

 by transverse partitions, into several chambers, which com- 

 municate with each other by triradiated apertures. 



128. S. lineaia, — Shell convex above, flat beneath, with a 

 central cavity on both sides. 



Helix lineata dorso convexo umbilicata margine acuto, Walk. Test. Min. 



8. t. l.f. 28 Nautilus lacustris, Lighffoot, Phil. Trans. 1786, 160. t. 1. 



f. 1, 7. Mont. Test. Brit. 191. t. vi. f. 3 — On aquatic plants in ditches, 



England. 

 Breadth scarcely a quarter of an inch, glossy, horn-coloured, with a whitish 

 spiral line at the junction of the whorls above ; whorls below, flat, with an 

 acute margin ; aperture obliquely semioval, the lips clasping the body ; cham- 

 bers distant, three in the body-whorl ; partitions of three subtriangular dis- 

 tinct plates, two lateral and one on the central side ; these partitions form 

 white centroperipheral lines externally. 



