172 PNEUMONOBRANCHIATA. 



Animal white, with two black lines ; mantle white, 

 speckled with black. 



Shell varying from one fifth to one sixth of an 

 inch in diameter, somewhat like Z. crystalling but 

 larger, more convex, and less shining, the whorls 

 less closely set, and the outer one larger in propor- 

 tion to the rest : the umbilicus is also larger. 



Mr. Jeffreys considers it as a variety of H. nitidula, 

 but Mr. Alder justly observes, that it differs from 

 that species in being scarcely one third the size, of a 

 different colour, and without any trace of opacity 

 underneath. This species preserves its characters 

 unchanged even when living in the midst of its 

 allies. 



Ferussac refers to H. nitidula a. Drap. for this 

 species. There is no such variety. Var. ft. of that 

 author, which Mr. Alder thinks he evidently intended 

 to refer to, is his H. radiatula. His species has 

 neither been figured nor described; but Mr. Alder ob- 

 serves that the specimens in his cabinet are undoubt- 

 edly the horn-coloured variety of H. pura. (1. c. 108.) 



Mr. Alder observes, " Dr. Turton's figure of 

 H. pura (f. 43.) is not a bit like the shell; it is 

 five or six times too large, and the wrong colour. 

 If intended to be magnified, it .should be so stated, 

 and a figure of the natural size put alongside." 

 (Letter, May 30.) 



51.8. ZomTEsnitidulus. Dull Snail, (t. . f. 136.) 

 Shell nearly flat, deep yellowish horn-colour, 

 sub-pellucid, rather strongly wrinkled, of a dull 

 waxy appearance above, more shining below, 

 except near the umbilicus, around which it is of 



