MOLLUSCA. PULMONIFERA. 
m 
AQUATICA. 
Tentacula tzvo, usually jlat^ with eyes at the base. Respire at 
the surface of the water. Sexes united ; spawn deposited 
under water on aquatic plants. Phytivorous. 
a. Shell spiral. 
b. Shell tun-ited. 
e. Whorls dextral. 
Limnea. 
Assiminia. 
cc. Whorls sinistral. 
Physa. 
Aplexa. 
bb. Shell discoid. Tentacula filiform. 
Planorbis. 
Segmentina. 
aa. Shell simple, conical. 
Ancylus. 
Gen. XXIX. LIMNEA. — Aperture of the shell longitudinal ; 
the outer lip, in bending in on the piUar, forming an oblique 
entering fold. Tentacula lanceolate. 
* Shell turrited. 
105. L. stagnalis. — Whorls six or seven ; the last large in 
proportion. 
Bucc. longum 6 spirarum, List. An. Ang. 137. Conch. Tab. 123, f. 21. — 
B. stag. Mull. Verm. ii. 132. — Helix stag. Penn. Brit. Zool. iv. 138. 
tab. Ixxxvi. f. 136. Mont. Test. Brit. 367.— In lakes and stagnant 
waters. 
Length nearly 2 inches ; brownish, translucent ; lines of growth distinct, 
with numerous longitudinal wrinkles ; the upper whorls smooth ; the separat- 
ing line distinct. Lister mentions having seen a variety with branched ten- 
tacula. 
106. L. fragilis. — Whorls six, diaphanous ; upper whorls 
with a shallow oblique separating line. 
Helix fragilis, Mont. Test. Brit. 369, tab. xvi. f. 7»— In canals in Eng- 
land and Ireland. 
This species is less than the preceding ; the aperture is narrower ; the 
spires increase more gradually, and the first formed ones are less rounded. 
It was observed by Montagu, in the Kennet and Avon Canal, Wiltshire. It 
likewise occurs in the Grand Canal near Dublin. The specimens I possess 
were sent to me by Dr Leach, from the Croydon Canal. 
107. L. detrita. — Shell thick, obtusely conical, of six whorls, 
with a brown band along the line of separation. 
VOL. I. 
s 
