Maryland Geological Survey 429 



of T. perforata have no specific significance. This ppecios grades into 

 T. multistriata, the extreme development in size and plicating. The last- 

 named feature varies in number from twenty-eight to forty-two, and the 

 dorsal fold may be low and rounded or greatly elevated and rounded or 

 subangular ; the ventral sinus is always broad and pronounced, and may be 

 regularly concave or subangular. The Maryland specimens have from 

 twenty-five to thirty-six plications. 



Length 1.5 cm. ; width 2 cm. 



Occurrence. — Heldeejberg Formation, New Scotland Member. 

 Corriganville, Devil's Backbone, Dawson, 21st Bridge, Maryland; Keyser, 

 West Virginia. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



Trematospira deweyi (Hall) 

 Plate LXXIII, Figs. 5-7 



Waldheimia deweyi Hall, 1857, Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., 



p. 89. 

 Trematospira (Rhynchospira) deioeyi Hall, 1859, Nat. Hist. N. Y., Pal., vol. 



iii, p. 216, pi. xxxvi, figs. '3a-3h, 1861. 

 Parazyga deweyi Hall and Clarke, 1893, ibidem, vol. viii, pt. ii, p. 128, fig. 



112, pi. xlix, figs. 40-46. 



Description. — -" Shell depressed subglobose, sometimes subquadrilateral 

 with the sides curving, moderately compressed ; valves nearly equal : 

 ventral valve a little the most prominent towards the umbo, having a 

 narrow faint sinus from near the beak to the front, where it sometimes 

 produces a slight sinuosity; beak apparently not perforate, extending a 

 little beyond the opposite beak, upon which it is closely incurved : dorsal 

 valve symmetrically arched. Surface marked by about forty regular 

 simple rounded striae, crossed by indistinct lines of growth, and, near the 

 front, occasionally by stronger imbricating concentric marks indicating 

 interrupted stages of growth. [Shell granulose.]" Hall, 1857. 



Hall and Clarke referred this species to their genus Parazyga, but as 

 T. deweyi has no hirsute exterior and, further, because T. equistriata is 

 referred by the same authors to Trematospira (both forms are very closely 

 related) , it seems better to refer both to the latter genus. T. deweyi is less 

 transverse and more biconvex than T. equistriata. 



