HELIX. 



103 



measurements of a large specimen: Greater diam. 9, lesser 8; 

 height 4 mill. I am much inclined to consider this a distinct 

 species, but remark upon it, as I believe it is more commonly 

 found in cabinets under the name of dorfeuilliana, than the shell 

 described by Lea. 



H. dorfeuilliana, and also the shell last considered, have a 

 tubercle within the aperture very similar to that in fastigans and 

 troostiana. 



Helix acutedeiitata, W. G. Binney. — Shell rimately umbilicated, 

 discoidal, equally flattened above and below, white, smooth, shining ; 

 spire very short, scarcely elevated, sunken, the apex about on a level with 

 the top of the last whirl ; whirls six, the upper five 

 gradually increasing, the last very large, inflated, Fig. 179. 



descending towards the aperture, below inflated, 

 rimate, showing only one and a half volutions, and 

 with a small deep umbilicus ; aperture small, very 

 oblique, subreniform ; peristome white, thickened, 

 acute, subreflected in its whole circuit, its ends 

 approached, joined and made continuous by a heavy 

 white, emarginate, excavated, prominent callus on 

 the parietal wall, extending almost across the aper- Helix acutedentata. 

 ture, its columellar margin with one or two short, 



perpendicular, marginal denticles; within the right hand margin of the 

 aperture are two horizontal lamina-like denticles, one obtuse, the upper 

 raised at its end into an acute, curved, long, hook-like point ; behind the 

 peristome on the outer surface of the last whirl the position of these 

 laminae is marked by two pits, between which the shell is pinched into a 

 sharp ridge joining the peristome. Greater diam. 14, lesser 11 ; height 

 4 mill. 



Helix acutedentata, W. G. Binnet, Proc. Acad. Nat. Sci. Philad. 1857, 



183; Terr. Moll. U. S. IV, 23, pi. Ixxvi, f. 1.— Pfeiffer, Mon. Hel. 



Viv. IV, 351. 

 Helix loisa, W. G. BrNNET, Proc. Acad. Nat. Sci. Philad. 1857, 183; 



Terr. Moll. U. S. IV, 23, pi. Ixxvi, f. 2.— Pfeiffer, Mon. Hel. Viv. 



IV, 351. 

 Dcedalochila acutedentata, Tkton, Am. Journ. Conch. Ill, 65, pi. x, f. 11, 



13 (1867). 

 Ikedalochila loisa, Trton, /. c. f. 12, 14. 



Mazatlan and Guajmas. • 



