206 Systematic Paleontology — Middle Devonian 



iiuu'li extended on the hinge and so iiuu Ii larger that I do not think tliey 

 can be referred to A. unibonata. Thinlc about making it a variety if 

 after a study of the material you can find characters sufficiently constant." 

 The specimen was later submitted to Dr. J. M. Clarke who apparently 

 referred it to this species since he wrote " Wliv not Ambocoelia praeum- 

 hona Hall ? " After this study it appears better to the writer, at present, 

 to refer these specimens with a question to .1. pracumhona. 



Length, 14 mm. ; width, 18 mm. 



Occurrence. — Eomney Formation, Hamilton Member. Ernstville. 



Collection. — Maryland Geological Survey. 



Family ATHYRIDAE 



Genus NUCLEOSPIRA Hall 

 XUCLEOSPIRA CONCINNA Hall 



Plate XX, Figs. 12-15 



Atrypa concinna Hall, 1843, Geol. N. Y., pt. iv, p. 200, fig. 3. 



Nucleospira concinna Hall, 1859, Twelfth Rep. N. Y. State Cab. Nat. Hist., 



pp. 25, 26. 

 Nucleospira concmna Hall, 1867, Pal. N. Y., vol. iv, p. 279, pi. xlv, figs. 33-57. 

 Nucleospira concinna Keyes, 1S91, .Tohns Hopkins Univ. Circ, vol. xi, p. 29. 

 Nucleospira concinna Hall and Clarke, 1893, Pal. N. Y., vol. viii. pt. ii, p. 145, 



fig. 131; pi. xlviii, figs. 12-17, 19-34: pi. Ixxxiv, fig. 38. 

 Nucleospira concinna Schuchert. 1897, Bull. U. S. Geol. Surv., No. 87, p. 273. 

 Nucleospira concinna Clarke, 1903, N. Y. State Mus., Bull. 65, p. 263. 

 Nucleospira concinna Grabau and Shlmer, 1909, N. Am. Index Fossils, vol. i, 



p. 349, fig. 454. 



Description. — Shells fairly small; bi-convex; nearly circular in out- 

 line, the width being usually a little greater than the length; valves sub- 

 e(|ual ; hinge-line about one-third, and sometimes half as long as the 

 width of the shell. Ventral valve regularly convex, the greatest con- 

 vexity a little above the middle curving regularly to the sides and front; 

 umbo ))rniiiincnt. the lieak pointed and incurved over the apex of the 

 dorsal valve: there is geneially a luu'i-ow depressed line from the beak to 

 the front of the valve. Dorsal valve regukrly convex, becoming a little 

 depressed toward the fnmt, the greatest convexity a little above the cen- 

 ter; there is usually a depressed line along the middle of the valve. 



