576 NEW YORK STATE MUSEUM 



at the latter place with a remarkably strong development of the 

 «ulci, which extend nearly to the ventral margin, leaving the 

 middle lobe projecting as a prominent sharp ridge. 



Upper Utica shale of Green Island and Menands, Albany co. 

 N. Y. 



3 O t e n b 1 b i n a s u b r o t u n d a sp. n. {see pi. 2, fig. 

 1,2,3,4). 



E. O. TJlrich, who made an exhaustive study of these forms and 

 described the species of C t e n o b o 1 b i n a occurring in the Cin- 

 cinnati beds, reports also two new species from the Trenton beds 

 of Minnesota (49:674, 675). To these can be added a new ^species 

 found in the middle Trenton shales of Port Schuyler (station 23). 



Valves shortly subovate, strongly convex, dorsal margin nearly 

 straight; ventral part approaching a semicircle in outline; sulcus 

 wide and deep, beginning near the middle of the dorsal margin, 

 oblique, curving backward below, dividing the carapace into two 

 subequal lobes, which are broadly connected in the ventral 

 region, the posterior lobe distinctly rounded and inclined to be a 

 little larger than the anterior; both lobes equally convex, with a 

 thick (?) edge anteriorly and posteriorly; surface minutely 

 granulose. 



Dimensions. Length .56 mm, hight .37 mm, thickness .17 mm; 

 length of a smaller carapace, .48 mm, hight .34 mm, thickness .20 

 mm. 



These minute valves are undoubtedly closely related to the two 

 Trenton species of Ctenobolbina described by ITlrich. 

 They fully agree with them in the presence of only one sulcus 

 which is strongly curved and of two bordered lobes; but they 

 differ from the one (Ct. fulcrata) in having the posterior 

 bulb already farther advanced, and from the other (C t. crass a) 

 by the lesser development of the border and the shorter, more 

 rotund outline. Ctenobolbina subrotunda differs 

 from C t . d u r y i , S. A. Miller ep. [Cin. quart, jour. set. 1874. 

 1 :232), a similar form from the "Hudson river group" of Cincin- 

 nati in being relatively much higher and having the sulcus more 

 medially located. 



