GUELPH FAUNA IN THE STATE OF NEW YORK 73 



Volutions 9-10. These are but slightly overlapped, their exposed surfaces 

 thus being quite regularly convex ; the upper slope is slightly flattened or 

 depressed to the obscure slit band. The sutural slopes are deep, the suture 

 itself narrowly impressed, the edge of the lower whorl being slightly 

 depressed against the whorl above. Umbilicus covered. Aperture oblique 

 or subfusiform in outline. Inner lip somewhat thickened, outer lip with a 

 deep linguiform emargination at its upper third. This is the edge of the 

 slit band, which is a gently depressed sulcus without sharp margins, at which 

 the surface lines are bent deeply backward. This band is evident on all 

 whorls even on internal casts as an obscure flattening modifying the contour 

 of the shell. The surface bears a multitude of fine and crowded, somewhat 

 irregularly concentric lines, which are profoundly reflexed at the slit band 

 but seem to be continuous over that area. On the lower slope of the body 

 whorl is evidence of a second revolving band, which does not, however, effect 

 any change in the direction of the concentric growth lines. This is a feature 

 which is well defined only in a single specimen other examples, whether 

 exteriors or internal casts, not showing it. 



Dimensions. The most complete example before us has a length of 

 85 mm, a width at the base of 28 mm. A large specimen, incomplete 

 at the apex, had a probable length of 100 mm and a basal diameter of 

 30 mm. 



Observations. This graceful and striking species is one of the most 

 abundant organisms in the Guelph horizon at Rochester. The Arey collec- 

 tion contains 25 or 30 specimens which are either internal casts in white 

 chert or retain the shell more or less completely in pulverulent white silica 

 with dolomitic interiors. The species has also been obtained in the upper 

 Shelby horizon. 



Shells of similar character to this have been already described from the 

 Guelph fauna. Dr Whiteaves has given figure and description ' of an 

 internal cast having similar outline and contour to H. whiteavesi though 

 of smaller size, and this he has identified with the Loxonema magnum 



1 Paleozoic Fossils'. 1884. v. 3, pt i, p. 17 ; 1895. pt 2, p. 87. 



