Maryland Geological Survey 427 



Genus TREMATOSPIRA HalP 



Trematospira simplex Hall ? 

 Plate LXXIII, Figs. 1, 2 



Trematospira simplex Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 211, pi. 



xxviila, figs. 2a-2f. 

 Trematospira simplex Hall and Clarke, 1893, ibidem, vol. viii, pt. ii, pi. xlix, 



figs. 17, 18. 



Description. — " Shell transversely elliptical or subrhomboidal, nearly 

 once and a half as wide as long: hinge-line scarcely declining from the 

 beaks ; cardinal extremities rounded : valves moderately and almost equally 

 convex, closely compressed at the latero-cardinal margins. Ventral valve 

 having a well-defined mesial sinus, which extends more than half way 

 from beak to base: beak elevated, scarcely incurved, and vertically 

 truncated by a small perforation, between which and the hinge-line is a 

 well-defined deltidium. Dorsal valve moderately convex in the middle, 

 and slightly elevated towards the front of the shell : beak closely incurved 

 beneath the deltidium of the opposite valve. 



" Surface marked by four or five simple plications on each side of the 

 center, two of which on the ventral valve are involved in the sinus ; and 

 three upon the opposite valve, the central one being broader and flattened 

 towards the base : entire surface granulose or punctate, with faint indica- 

 tions of growth lines." Hall, 1859. 



Length 9 mm. ; width 12 mm. 



Of this species but a single specimen has been seen. It is a sharp cast 

 of the interior and is, therefore, a little more rounded posteriorly than is 

 the case with the Tennessee specimens. The plications are sharply 

 angular, simple, and none show any tendency to bifurcate. With more 

 material it may prove to be distinct. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Devil's Backbone. 



Collection. — George M. Eoeder. 



^ See Hall and Clarke, 189.3, Nat. Hist. N. Y., Pal., vol. viii, pt. ii, p. 124. 



