Descriptions of Devoxian Fossils. 239 



half, ronnded above and entirely concealed by the unibiliens. The 

 volutions are sometimes marked bv strong, subregular, transverse folds 

 or wrinkles, crossing from the suture obliquely backward to near tlie 

 angle at the base of the whorl, but always strongest near the suture. 



There is much difference in the general form among individuals 

 referred to this species, often, perhaps, owing to distortion after 

 being imbedded ; but some of them appear to have had a much higher 

 spire than others, as in the case of a small specimen hgured. In some 

 examples the suture is close, while in others it is very distant. There 

 is, also, much variation in the strength of the transverse folds and in 

 the degree of flattening on the under side of the volution ; but as none 

 of these characters appear to be constant, they have been considered 

 only as variations of the same species. 



Genus — CKYPTO^^ELLA Hall. 

 Gbyptonella Calvini n. sp. 



The species of Cry])tonella referred to on page 225 as C. Eudora 

 proves on the examination of more perfect specimens to be entirely 

 distinct from the New York species, and we therefore propose for it the 

 name C. Calvini. The shell is much less ventricose than C. Eudora, 

 is often broadest below the middle, and usually has the median area 

 of the dorsal valve elevated near the front margin. The best speci- 

 mens were obtained at Hackberry, Iowa, by Prof. S. Calvin, of Dubuque. 



Genus — STROPHODONTA Hall. 

 Strophodonta hybeida n. sp. 

 Shell of medium size, resupinate ; hinge line equal to or shorter than 

 the shell below ; valves closely appressed to each other ; area of mod- 

 erate width, distinctly crennlate exteriorly. Surface marked by irreg- 

 ular and often indistinct radiating striae, which are strongest near the 

 umbones and are frequently interrupted by the stronger lines of growth, 

 where they bifurcate, and become finer toward the front of the shell. 



This species resembles S. reversa Hall, but attains a larger size, is 

 always flatter, more finely striated, is a thinner shell, less arcuate, and 

 has differently formed muscular impression. 



Obtained at Hackberry, Iowa, from rocks of the age of the Chemung, 

 by Prof. S. Calvin. 



