GASTEROPODA. 123 



pah/h/s, figure 22 of same plate, and in figure 6 of plate 24; but it is not 

 pustulose in any specimen observed. 



The shell is smaller than B. patulus, and, in the absence of the dorsal band, 

 has much the same aspect as that species. 



CYRTOLITES, Conrad. 



Subgenus Cyrtonella. 



Shells ovoid, trumpet-shaped. Volutions one or more in the same plane : 

 apex minute, making about a single turn, and rapidly expanding beyond; 

 peristome entire ; dorsum angular or subcarinate. Surface sculptured. 



The two following forms have the general character of the genus Cyrtolites, 

 as described and illustrated by Mr. Conrad. They differ from all the described 

 species, in the much more rapid expansion of the outer volution; but the direct 

 or nearly direct transverse striae in one species, the general surface ornamenta- 

 tion, and the essential absence of a sinus in the anterior margin of the peris- 

 tome, are characteristics of the genus Cyrtolites. It is somewhat remarkable, 

 however, that no species of the genus is known to occur in any of the forma- 

 tions between the Hudson River group and the Hamilton group, while the 

 conditions of the Clinton, Niagara and Lower Helderberg groups would seem 

 as favorable to their existence as the Hamilton. The recurrence of these 

 forms, therefore, under such circumstances and after so long an interval, 

 demands the most critical inquiry regarding their generic relations. 



Cyrtolites (Cyrtonella) mitella. 



PLATE XXV, FIGS. 23-28. 



tAite$1 mitella. Ham. Descriptions of New Species of Fossils, etc., p. 33. 1861. 

 Fifteenth Rep. N. Y. State Cal>. Nat. Hist., p. 61. 1862. 

 •• " •■ Illustrations of Devonian Fossils : Gasteropoda, pi. 25, figs. 16-18 only. 1876. 



«• ji'ilml us, " Illustrations of Devonian Fossils: Gasteropoda, pi. 25, figs. 22-24. 1876. 



Shell arcuate, subovoid, making altogether less than two volutions in the same 

 plane; the first volution very minute; the body-whorl rapidly expanding 

 to the aperture, which is nearly circular ; the peristome scarcely spreading; 



