108 MALACOZOA. GASTEROPODA. PULMOBRANCHIATA. 



green, olivaceous, or blackish-green colour, usually variegated 

 with light brown or yellowish-grey. It is thicker and much 

 less transparent than that of the last species. 



Common, in ditches, pools, and rivers ; generally distributed. 



Limnaeus pereger. Drap. Moll. Terr. et. Fluv. 50. PI. 2. f. 34, 

 35. Buccinum peregrum. Muller, Moll. Terr, et Fluv. 130. 

 Lymnsea peregra. Lamk. Syst. vi. 2. 161 ; Ed. n.viii. 413. Helix 

 peregra. Gmel. Syst. Nat. 3659. Helix putris. Penn. Brit. 

 Zool. iv. 139. PL 86. f. 137. Lymnaea peregra. Brown, Tllustr. 

 PL 42, 36, 38. Limnaea limosa. Flem. Brit. Anim. 274. Lim- 

 naeus pereger. Gray's Turton. 233. Helix peregra. Mont. Test. 

 Brit. 373. PL 16. f. 3. 



C. Limn&us pereger limosus. Brook Mud-Shell. 



Shell ovato-oblong, very thin, brittle, semitransparent, 

 glossy, with the spire short ; the aperture oval-oblong, acute 

 behind, two-thirds of the whole length ; the last turn oblique, 

 very faintly striated transversely ; the colour light brown. 

 Length about five-twelfths of an inch, breadth about half the 

 length. 



The animal has the head and foot greyish-green, the hind 

 part of the collar variegated with black ; the rest of the body 

 black, spotted with light brown. 



Although brown, the shell is so transparent that an object 

 can be seen through it. When it contains the animal, it ap- 

 pears black, with brown spots. 



Helix limosa. Linn. Syst. Nat. 1249. Helix limosa. Brown, 

 Wern. Trans, ii. 530. PI. 24. f. 11, 12; Illustr. PL 42. f. 39, 40. 

 Limnaea limosa. Flem. Brit. Anim. 274. 



It occurrs in brooks, and marshy places. Powis Burn at 

 Old Aberdeen ; Ditches with running water near the same 

 place ; Burn of Cruden ; Auchmedden. 



There certainly is much difference in form and size between 

 the largest and broadest individuals of Limnaeus ovatus, and 

 the smallest or narrowest of Limnseus limosus ; yet the three 

 supposed species so graduate into each other that, I think, 

 they must be merely races or varieties. Many more might be 

 given, were one so disposed; but the task would be useless. 

 It appears to me that we have but one species, which varies in 

 the size, colour, and thickness of the shell, according to cir- 

 cumstances. The larger and more ventricose it is, the shorter 

 is the spire. In still water, especially if of great extent, it 

 assumes the form of Limnoeus ovatus ; in running water, espe- 



