558 Systematic Paleoxtology — rrPEu Devoxian 



Strophonella rcvcrsa Grabau and Shimer, 1909, N. Amer. Index Fos., vol. 

 i, p. 222, fig. 270. 



Description. — Strophonella is a stropheodontid in which the relative 

 convexity of the valves is normal in early growth but subsequently the 

 ventral valve becomes concave and the dorsal convex. Strop]/ onella 

 reversa is distinguished by its considerable size, coarse radial plications 

 in the umbonal region, almost or fully obliterated deltidium, denticulate 

 hinge, strongly elevated ventral muscle scars, thickened and sinused 

 pallial region. 



AMiether or not the shell here under observation is a tme Strophonella 

 can not be fairly determined from the single interior of the dorsal valve 

 in the collection. Nevertheless it is directly comparable with the species 

 above cited as it shows a surface curvature normal to the younger 

 conditions of that species where the primitive concavity of the dorsal 

 surface is gradually changing to convexity about the margins. The in- 

 ternal markings are those of the species and in addition thereto the shell 

 bears the median often irregular depression of the surface which is always 

 noteworthy in S. reversa. 



Length 17 mm.; width 25 mm. 



The single specimen recorded is from the region a few miles south of 

 Oakland. Strophonella reversa is common iu the upper Devonian of 

 Eockford, Iowa, of rare occurrence in the Chemung of ISFew York. 



Occurrence. — Jennings Formation, Chemung Member. South of 

 Oakland. 



Collection. — Maryland Geological Survey. 



Strophonella sp. 



Description. — An individual of this genus, which is too poor for specific 

 identification, has been observed at the locality given. 



Occurrence. — Jennings Formation, Chemung Member. National 

 Eoad west of Frostburg. 



Collection. — Marvland Geological Survev. 



