CANADIAN FOSSILS. 21 



M. HELICTERES, N. Sp. 



Plate IV. Fig. 2-4. 



M. turrita, biuncialis, avfractibus 5 sub-rotunda tis, tricarinatis anfiquatis, 

 ultimo vago : carinis omnibus obtusis, mediand (cingulo) lata ; striis 

 crebris asperis. 



This shewy species is not more remarkable for the irregular uncoil- 

 ing of the last whorl (resembling in this respect certain varieties of 

 the common snail, Helix aspcrsa*), than for the rough striation and 

 antiquated appearance of the whorls. 



The band or principal keel is broad and flat, the upper and lower 

 edges being prominent, and the middle only a little convex ; the 

 rounded notch is rather deep. The upper and lower keels are obtuse, 

 and equally distant from the band, the upper placed about half-way 

 towards the suture, which is not at all channeled ; its edge on the 

 free whorl shews as an obtuse ridge. See fisure 3 s. 



The spire is pyramidal, but the separate whorls are rounded ; the 

 upper ones have the inferior carina covered by the suture, but it 

 is exposed in the lower one by the divergence of the last whorlt 

 figure 2, which afterwards becomes quite free, figures 3, 4. 



The striation is very rough and coarse ; the lines of growth cross- 

 ing the ridges, give these an antiquated appearance. The mouth is 

 round ; the shell thickened, especially on its inner side. 



In the thick, obtuse whorls, coarse striation, and broad band, this 

 epecies a good deal resembles M. semirotunduta, McCoy, from the 

 Caradoc formation of N. Ireland, but that species is destitute of the 

 upper keel, besides having much rounder and more ventricose whorls. 



M. tricarinata, Hall, (Pal. New York, vol. i., plate 38, fig. 6,) is a 

 Trenton species much more resembling our shell ; but his specimens 

 are too imperfect to identify with, particularly as he mentions 

 nothing of the tendency to uncoil, and distinctly says there is no 

 umbilicus ; the carinae, too, are represented as sharper than those of 

 our species. Moreover, the mouth is said to be ''acutely" produced 

 below. It has, however, similar sharp prominent striae, and is pro- 

 bably very nearly allied. 



Locality. — Common at Allumette Islands. 



See Gray's edition of " Turton's Manual of British Shells." (Vignette.) 



