SEGMENTINA. 
245 
f. 6. — Planorbis contortus. Muller ^ Verm. ii. 162.; Drap, 
p. 42. t. 1. f. 39 — 41.; Jeffreys., Linn. Trans, xvi. 383.; 
Rossm. Icon. ii. 16. t. 7. f. 117.; Turton., Man. ed. 1. f. 96. ; 
JBrard., p. 157. t. 6. f. 12 — 14.; Leach., Syn. Moll. 112.; 
Forbes and Hanley., B. M. iv. 160. t. 126. f. 3. — Helix um- 
bilicata. Pulteney., Dorset, t. 20. f. 11. — Helix crassa. Da 
Costa., B. S. t. 4. f. 11. 
Inhab. ditches. Common. 
Animal grey or blackish. {^Sturm, t. 41.) 
Shell about two tenths of an inch in diameter, 
and one tenth in thickness, brown horn»colour, and, 
when free from accidental incrustations, exhibiting 
in water a bronzed or gilt lustre ; volutions five, 
remarkably compact and equal in size ; the upper 
surface with a large and deep umbilicus; aperture 
very narrow, crescent-shaped, wider than high, only 
slightly produced on the under side. 
In describing this shell, Dr. Turton called that 
the upper side which was considered the lower in 
other species, and vice versa. 
9. Segmentina Flem. (Segment Shell.) 
Animal nearly like Planorhis^hvX the shell is polished, 
and the cavity contracted by permanent internal 
transverse ridges, having a triradiated opening ; 
lingual teeth very minute. 
So called from the internal segments or partitions. 
Mr. Alder does not think that the septa in the 
shell are sufficient to raise it to the rank of a genus, 
as the animal is exactly like Planorbis. Muller con- 
founded it as a variety with P. fontanus ; like that 
species, the spire is umbilicated, and the front of the 
shell has the appearance of being the proper spire. 
