Raymond: Gastropoda of the Chazy Formation. 201 



ing, bending backwards from the suture and forward in passing over the 

 edge of the shell ; aperture obtusely trigonal, depressed above, slightly 

 expanded beyond the dimensions of the whorl just behind it ; axis 

 hollow, umbilicus broad and deep, extending to the top of the spire." 



Operculum. — The operculum of Maclurites magnus has been referred 

 to by Billings, Ulrich, and others, but does not appear to have been 

 figured. As shown in the figures on Plate LII, the operculum is large, 

 heavy, horn-shaped, with the nucleus twisted to the right. In the 

 inner right hand corner of the operculum is a long process which pro- 

 jects downward into the shell and forms a place for the attachment of 

 muscles. The specimen figured was silicified and was removed from 

 the limestone matrix by etching. The inner side was exposed first, 

 and the drawing for figure 2, Plate LII, was made before etching was 

 complete, but the muscular process was imperfectly preserved. In an 

 attempt to free the shell entirely from the matrix the inner edge of the 

 shell was destroyed so that when figure 1 was made the specimen was 

 imperfect, but the outline is restored from the figure previously made. 

 Viewing the operculum from the outer side, the lines of growth are 

 very prominent and there is a slight depression extending from the 

 nucleus along the left margin to the lower left hand corner. Figure 

 1, Plate L, shows a view of the exterior of a calcified specimen from 

 Crown Point. On the right the shell has been removed and the 

 depression shown is the opening left by the removal of the basal por- 

 tion of the muscle-process. 



Locality. — This species is common in the Chazy Limestone from 

 Orwell, Vermont, to Montreal, Canada. It occurs also in Eastern 

 Tennessee. The figured specimens are in the Carnegie Museum. 



Maclurites atlanticus Billings. 

 Maclurea atlantica Billings, 1859, Canadian Naturalist and Geologist, 



Vol. IV, p. 459. 



This species was described from specimens obtained at the Mingan 

 Islands and was separated from Maclurites magnus by the difference 

 in form of the operculum. No specimens of this species have been 

 found in the region of Lake Champlain. The following is Billings' 

 original description : 



" Maclurea atlantica. 



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

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



