320 Systematic Paleontology 



large, triangular, apparently mostly closed. Surface marked by regular, 

 rounded, slightly elevated, radiating strige: interior scarcely granulosa, 

 strongly marked with a plicated flabelliform muscular impression, cover- 

 ing nearly two- thirds of its extent." Hall, 1857. 



Length 2.5 cm. to 4 cm. ; width about 4 cm. 



This has been a very perplexing species, owing to the fact that the valves 

 are found separated, are very thin and frail, and usually broken before 

 deposition. This is shown in the ventral valves figured by Hall, no two 

 of which are alike, and one of which has the anterior margin passing 

 through the muscular scars (see fig. 2h, Hall), an impossible condition for 

 a living brachiopod. The mature shells attained a size nearly as large as 

 *S'. magnifica, are usually thin and quite convex. It is more often these 

 convex valves that have so much of the anterior region broken away, 

 though preserving the characteristic posterior portion with its very high 

 ventral cardinal area. The writer has before him twelve half-grown, not 

 very convex examples, seven of which have both valves united. The latter 

 show that the shells are very thin and that the ornamentation of the two 

 valves is very dissimilar. On the ventral valve the strige are low, obscure, 

 and separated by wide flat interspaces, there being rarely seven and more 

 comjnonly from nine to twelve of these in 5 mm. This valve appears 

 nearly smooth. The dorsal valve is marked by exceedingly fine, closely 

 adjoining thread-like strife, there being not less than thirty-two in 5 mm. 

 In New York it is usually this valve that is found in large examples, with 

 the anterior margin perfect, and is nearly always labeled 8. lincklceni. 

 However, this is now known to be the companion valve to S. magniventra, 

 which was based on ventral shells. The interior of this species is practi- 

 cally the same as in 8. magnifica. 



8. magniventra is easily distinguished from all associated Stropheo- 

 dontse by its external ornamentation, {. e., by tJie few widely separated 

 obscure strise on the ventral valve and by the very delicate and exceedingly 

 numerous strise of the dorsal valve. Another feature is the very high 

 ventral cardinal area. 



Occurrence. — Okiskany Formation, Eidgely Member. Cumberland. 

 South end of Martin Mountain, Miller's Spring near Cumberland. 



Collection. — Maryland Geological Survey. 



