110 MALACOZOA. GASTEROPODA. PULMOBRANCHIATA. 



fragilis. Linn. Syst, Nat. i. 1249? — Lymnaea palustris. Lanik. 

 Syst. vi. 2. 162; Ed. n. viii. 409. — Limuaea palustris. Flera. Brit. 

 Anim. 274. — Lymnaea palustris. Brown, Illustr. PI. 42. f. 17, 18. 

 ■ — Linmeeus palustris. Gray's Turton. 



3. LimncBUs truncatulus. Little Mud-Shell. 



Shell ovato-oblong, conical, pointed, thin, horny, semi- 

 transparent, of about six turns, which are well rounded, deeply 

 separated by the suture, somewhat abruptly curved at the 

 upper margin, transversely striate, the last turn large with 

 faint longitudinal ridges ; the mouth ovato-oblong or ovate, 

 rather obtuse behind, nearly half the length of the shell, with 

 the pillar-lip expanded so as partially or entirely to cover the 

 umbilicus ; the colour varying from yellowish-grey to umber 

 or dusky purplish-brown, that of the interior from horn-colour 

 to purplish-brown, of the inner lip from white to purple. 

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

 height. 



It differs from Limnseus palustris in having the turns of the 

 spire more convex, and somewhat abruptly bent toward the 

 suture. Muller has clearly expressed this character. " An- 

 fractus quinque, quilibet, qua majorem spectat, declinatus, 

 qua minorem truncatus est, quo caractere a reliquis europasis 

 differt." 



Generally distributed, occurring abundantly in pools, rivers, 

 brooks and rills ; as in Hilton Quarries, the mill-pond near 

 the New Bridge of Don, the Inverury Canal, and similar places, 

 from the coast far into the interior. 



It presents very great differences in size and form, the de- 

 gree of smoothness or rugosity, the outline of the mouth, the 

 extent of the inner lip, the prominence of the spire, which is 

 frequently truncate or eroded. The most remarkable varieties 

 are the following : — > 



A. Limnmis truncatulus oblongus. Common Little Mud-Shell. 



Shell ovato-oblong, pointed, with the turns moderately con- 

 vex, thin, glossy, distinctly striulate ; the mouth oval-oblong, 

 the inner lip expanded and reflexed ; the umbilicus generally 

 covered, but sometimes distinct ; the colour light purplish- 

 brown, of the interior yellowish-brown, of the inner lip 

 pinkish. 



This variety is common in clear still water ; as the pools in 

 Hilton Quarries, 



