Fossils of the Chazy Limestone. 459 



angularity. Owing to the thickness of the shell the sutures above 

 the body whorl are not deep, and the upper whorls are in conse- 

 quence not ventricose, but still encircled with the band — appa- 

 rently, also, with the upper carina. In the cast the whorls are 

 smooth rounded ventricose, and exhibit scarcely any trace o* 

 either the band or the carina. In some specimens the shell on 

 the body whorl exhibits some deep, irregular undulations of 

 growth. 



Resembles both M. helicteres (Salter) and M. bicincta (Hall) ; 

 but these species have a distinct carina below the band. 



Locality and Formation. — Mingan Islands. Chazy. 



Collectors — Sir W. E. Logan, J. Richardson. 



The other gasteropods of the Chazy are two species of Holo- 

 pea and Trochonoma umbilicata (Hall, sp.) 



Maclurea Atlantica, (N. s.) 



Description. — Whorls about four, flat or gently convex on the 

 lower side, ventricose above, and obtusely angulated at the edge 

 of the umbilicus. In a specimen with four whorls the diameter 

 is three inches and seven lines ; the width of the last whorl at 

 the aperture, on the flat, lower side, is sixteen lines; at the termi- 

 nation of the third w T horl six lines, and of the second whorl three 

 ines. The first whorl occupies about two lines of the diameter 

 in the centre. In the same specimen, if on a line drawn from 

 the aperture straight across the shell, the width from the outside 

 of the aperture to the centre is two inches and two lines, and 

 from the centre to the termination of the line on the posterior 

 side one inch and three lines. 



When the above dimensions are compared with those of 

 Maclurea Peachii (Salter), as figured in the Quarterly Journal of 

 the Geological Society, vol. 15, plate 13, fig. la, the difference 

 between the species at once becomes obvious. That figure repre- 

 sents a specimen of M. Peachii, which is exactly three inches 

 and seven lines in diameter; but it has five whorls, the width of 

 the last one at the aperture being twelve lines, and of the others 

 measured on the same line 6, 3, lj and 1 lines respectively. 

 M. Peachii is, therefore, a distinct species, differing from ours by 

 its more numerous and more slender whorls. 



The operculum found associated with the specimens is elon- 

 gated, flat or a little concave on one side, moderately convex on 

 he other, curved like a short Cyrtoceras, but not in the same 



