126 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



(Semper, Phil. Archip.) ; also Z. Gundlnchi^ which, however, has some of its 

 marginals even tricuspid, and tricuspid laterals. 



The American form here under consideration was described by Mr. Say 

 under the name chersina. Judtjing from its shell alone, it seems identical with 

 the European Z.fulvus. It has thus been considered one of the circumpolar 

 species common to the three continents, and is so treated above. My confidence 

 of this identity, however, is now shaken by a study of the description and 

 figure by Lehmann (Lebenden Schnecken, etc., p. 79, PI. X. Fig. 24), of the 

 dentition of the European Z. fulvus. He gives 86-100 rows of 25 — 1 — 25 

 teeth ; the first two laterals he makes tricuspid, while they are only bicuspid in 

 our form. The marginals appear to be bifid. The question of identity must 

 therefore, I fear, be considered as still open. 



It is found under, and in the interstices of wet, decaying wood, under layers 

 of damp leaves in forests, and under fragments of wood on the borders of 

 ponds. 



The above-named localities prove this to be a widely spread species. Its 

 diminutive size has probably prevented its being observed in other places. It 

 offers but few varieties, and is easily distinguished by its conical form, and 

 thin, amber-colored, transparent shell. It is a very beautiful and delicate little 

 species. The spire is elevated, turreted, attaining even seven full volutions, 

 with an obtuse apex ; at other times it is much lower, with a somewhat pointed 

 apex, and not exceeding five volutions. In the latter case, the base is of course 

 much broader in proportion to the height, and the outer whorl is obtusely cai-i- 

 nated. This carinated form is //. egena of Say, of which Dr. Binney writes: — 



" I have recently examined the original specimen of the shell described by 

 Mr. Say as Helix egena, and by him deposited in the collection of the Academy 

 of Natural Sciences, in Philadelphia. I could not, on careful comparison, detect 

 any difference between it and the depressed variety of H, chersina. Mr. J. S. 

 Phillips, the obliging curator of the department of Conchology in that institu- 

 tion, joined me in the opinion that the two are clearly identical." The elevated 

 form only is figured in the "Terrestrial Mollusks." It is interesting to state 

 that in Europe also these two extreme forms are known to exist, the analogue 

 of egena being called Mortoni (Jeffreys). 



The plane of the base is so nearly horizontal that the shell, when set upon 

 its base, is upright. It is so transparent that some of the sutures of the spire 

 are visible through the substance of the shell, when viewed on the base. 



There is a variety with an internal tooth. 



Zonites Fabricii, Beck. 



Shell subimperforate, conical, thin, lightly striated, pellucid, reddish ; spire 

 conical, rather acute ; suture profound ; whorls 6, convex, narrow, the last 

 wider, rather convex at base, impressed at the centre ; aperture vertical, widely 



