Segmentina. MOLLUSCA. PULMONIFERA. S79 
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. cylindricus. — Cylindrical; left side concentrically striated ; volutions 
three or four, adpressed ; aperture oblong, quadrangular. — Smier. Min. Conch, 
f. 140. f. 2. — Fresh-water formation.^ Isle of A\^ight. 
2. P. obtusus. — Depressed ; left side most concave ; volutions embracing? 
slightly compressed on the right ; aperture obliquely and obtusely obcordate^ 
—Sofwer. Min. Conch, t. 140. f. 3. Isle of Wight. 
3. P. lens.. — Lenticular, subcarinated ; volutions embracing ; aperture very 
oblique, obcordate— (S'owcr. Min. Conch, t. 140. f. 4. Isle of Wight. 
4. P. hemestoma — Depressed, smooth ; right side convex, umbilicate ; left 
side flat ; aperture oblique, subtriangular. — Sower. Min. Conch, t. 140. f. 6. 
Plastic-clay^ Plumstead. 
5. P. radiatus. — Lenticular, radiated ; left side umbilicate ; volutions near- 
ly concealed; aperture obcordate — wSower. Min. Conch, t. 140. f. 5. Green- 
sands 
6. P. euomphalus. — Depressed, subcarinated ; concentrically striated ; right 
side flat ; left side largely umbilicate ; aperture subtriangular. — Sower. Min. 
Conch, t. 140. f. 7? 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. SEGMENTINA.— SheU divided internally 
by transverse partitions, into several chambers, which com- 
municate with each other by triradiated apertures. 
128. S. lineata. — 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, Lightfoot., Phil. Trans. 1786, 160. t. 1. 
£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. 
