Maryland Geological Survey 139 



The single specimen from Maryland shows mainly an internal impres- 

 sion of the ventral valve ; but on one side there is some of the shell clearly 

 showing the stronger striae with three or four much finer ones occupying 

 the interspaces. The specimen is considerably larger than the usual ones 

 of this species; but it was sho^vn to Dr. J. M. Clarke, who considered it a 

 large specimen of the above species. The muscular area is liigh and 

 sharply marked, a character which Dr. Clarke states is found in this 

 species as well as a somewhat similar one in the Maryland specimens of 

 Stropheodonta {Douvillina) cayiita Hall from the Jennings formation. 



This species is characterized by its small to medium size ; quite convex 

 ventral valve; long hinge-line with acute to auriculate extremities and 

 the surface marked by distinct distant striae between which aie several 

 much finer ones, scarcely visible to the naked eye. 



Length of Maryland specimen, 30 mm. ; width, 35 mm. 



Length of average New York specimens, 15-21 mm.; width, 25-38 mm. 



Occurrence. — Eomney Formation, Hamilton Member. East banlc 

 Evitts Creek below Wolfe Mill; B. & 0. E. R. cut at 21st Bridge ( ?).' 



Collection. — Maryland Geological Survey. 



Stropheodonta conga va Hall 

 Plate X, Figs. G, 7 



Strophomena {Strophodonta) concara Hall, 1857, Tenth Rep. N. Y. State Cab. 



Nat. Hist., pp. 115, 140, fig. 1. 

 Strophodonta concava Hall, 1867, Pal. N. Y., vol. iv, p. 96, pi. xiv, figs. 2a-2d; 



pi. XV, figs. 1-5; pi. xvi, figs, la-lh. 

 Stropheodonta concava Hall and Clarke, 1892, Pal. N. Y., vol. viii. pt. i, pi. 



xiv, figs. 16-23. 

 Stropheodonta concava Schucliert, 1897, Bull. U. S. Geol. Surv., No. 87, p. 420. 

 Stropheodonta concava Clarke, 1903, N. Y. State Mus., Bull. 65, p. 331. 

 Stropheodonta concava Grabau and Shinier, 1907, N. Am. Index Fossils, vol. 



ii, p. 216, fig. 261. 



Description. — Shell large, concavo-convex or subhemispheric. broadly 

 semielliptical or subcircular in outline; the hinge extremities are some- 



* In general a (?) mark following a locality indicates that the specimen from 

 that place is identified with a query. 



