CONTRIBUTIONS TO PALEONTOLOGY. 53 



the upper edge of the volution overlapping the next preceding 

 one, and constricted just beneath the margin, which is but faintly 

 or not at all marked by the longitudinal strise 



This species differs from the more common form of Loxonema of the 

 Hamilton group in the lesser convexity of the volutions, straightness of striae 

 (which, however, are more abruptly bent on the last volution), and the over- 

 lapping or banding of the upper margin of the volution at the suture-line. 

 One specimen examined retains nearly six volutions, and has a length of 

 one inch and a half; which would have been slightly increased, had the 

 lower extension of the columella been entire : diameter of last volution 

 half an inch. A specimen of the ordinary form, possessing six full volutions, 

 measures one and a quarter inches in length ; the six volutions from the 

 aperture reaching to the height of the fourth volution in the species under 

 consideration. 



Geological formation and locality. In shales of the Hamilton group : 

 Delphi, Onondaga county, N.Y. 



LOXONEMA HAMILTON.^. ^ f ^^ '^^ 



Loxonema nexilis : Geol. Report 4th District New-York, 1843, p. 201. 

 Not Loxonema nexilis of Phillips. 



Shell elongate, subulate. Volutions convex, about thirteen in the 

 largest specimens, very gradually increasing in size from the 

 minute apex, the last one ventricose. Aperture ovate, narrowing 

 below : columella extended. 



Surface marked by longitudinal sharp curving strise, which bend 

 backwards from the suture and forwards towards the base of the 

 volution, having the greatest curve near the middle : strise se- 

 parated by sharply defined grooves, which are a little wider than 

 the ridges; the strise increasing in distance as the shell grows 

 older. 

 A specimen showing thirteen volutions measures one inch and 



three-eighths in length, and the diameter of the last volution is half 



an inch. 



This species is the common form in the Hamilton group, and differs from 

 the preceding in the more numerous and more convex volutions, as well as 

 in the more strongly arched striae and more extreme attenuation of the shell. 

 I have heretofore identified this species with the L. nexilis of Phillips ; 

 but its form and proportions are intermediate between that and L. sinuosa, 

 while the striae are curved as in the latter species. The figures of Phillips 

 represent the striae a little curved backwards at their upper extremities, 

 with an enlargement just below ; features which our species does not possess 

 1861.] 



