GASTEROPODA. 51 



Isonema depressa is described as being "but little convex between the angular 

 periphery and the imperforate umbilical region ;" and the striae below the 

 periphery " suddenly become obsolete." 



The above features of genus and species are quite incompatible with the 

 following forms. 



Callonema bellatula. 



PLATE XIV, FIGS. 10-15. 



Loxonema bellatula, Hall. Fourteenth Rep. N. Y. State Cab. Nat. Hist., p. 104. 1861. 

 Isonema bellatula (H.) Mkkk. Proc. Acad. Nat. Sci. Phila., p. 252. 1865. 



" " " " Geol. Survey of Illinois, vol. 3, p. 443. 1868. 



" " " H.-W. Twenty-seventh Rep. N. Y. State Mus. Nat. Hist., pi. 13, f. 12. 1875. 



" " " Hall: Illustrations of Devonian Fossils: Gasteropoda, pi. 14. 1876 



Shell subovoid-conical ; spire elevated and rapidly expanding below. Volu- 

 tions about six or seven, the upper ones minute and somewhat gradually 

 expanding to the third or fourth, and more rapidly below, the last 

 one being very ventricose, regularly rounded or obtusely subangular 

 towards the base. Aperture apparently transverse — its extension below 

 not fully known ; columellar lip thickened,, spreading above and extended 

 anteriorly. 



Surface marked by regular, even, sharply-elevated striae, with about equal 

 interspaces, which are slightly turned backwards from the suture and 

 gently curved to the base of the volution, and on the last one curving over 

 the periphery with equal strength — a portion becoming obsolete, and 

 others coalescing and becoming stronger as they enter the umbilical 

 depression. 



The species presents the external characters shown in the figures 10-15 of 

 plate 14, and I can find no means of separation between those showing an 

 obtuse angularity at the base of the last volution and those which are regularly 

 rounded and ventricose. The surface striae are alike in the several examples. 



In figure 10, which seems to me not to be specifically distinct from the 

 others, the volutions are flattened upon the upper side for a narrow space 



