ZONITES. 93 



especially about the umbilicus, which is large and 

 very deep ; aperture oblong crescent-shaped, com- 

 pressed, oblique, as long as it is wide. 



Mr. Alder observes that continental specimens of 

 this shell are larger, and rather more open in the 

 umbilicus, than British ones, which induced M. de 

 Ferussac to think that they might be distinct. The 

 same remark is applicable to Helix nitidiila ; but in 

 both cases he thinks it amounts to nothing more than 

 a variety. H. nitens (Fer. Tab. Moll.) is only the 

 English variety of the species in a small state. 



H. nitens of Michaud, if we may judge from the 

 figures, is H. nitidula Drap. Mr. Alder suspects 

 Michaud's H. nitidula is, like that of Pfeiffer, the 

 H. nitidula var. yS of Drap., which is his H. radia- 

 tula. 



27. 3. ZoNiTES purus. Delicate Snail. — Shell de- 

 pressed, rather shining, transparent white, 

 slightly striated or wrinkled, with four shining 

 . whorls set diagonally ; under side more flattish 

 than the u[)per, and without any appearance of 

 opacity ; umbilicus rather large, (t. 4. f. 43.) 



Helix crystallina. FZem. 5. ^, 262. (?)— Helix vlridula. Menke, 

 Syn. 127.— Helix lenticula. Held. Isis, 1837, 304. — Polita 

 nitidosa and P. clara. Held. Isis, 1837, 916. — Hf-licella iiiti- 

 dosa. Beck, Ind. f. — Helix (dectrina. Gould, Boston Jour. 

 N. H. iii. 423. t. 22. f. 2. — Helix pura. Alder, Cat. 12. n. 

 46.; Mag. Zool. and Bat. ii. 108.; Turton, Man. ed. 1. 59. 

 (not the tiifure). — Helix nitidula var. /3. Drap. Moll. 117. 

 t. 8. f. 21, 2-2.; Jrffreys. Linn. Trans, xiii. 511.— Helix Alderi. 

 Bean, MSS., Brit. Mus. — Zonites purus. Gray, Man. 

 171. t. 4. f. 43.; Forbes and Hanletj, B. M. iv. 27. t. 221. f. 

 5, 6. — Z, (Aplostoma) purus. Moq. Tundon, Moll. Franc. 

 ii. 87. t. 9. f. 22. 25. 



