Maryland Geological Survey 185 



Keyes reported Ainjpa spinosa from the Hamilton of western Maryland' 

 and Prof. Schuchert listed it as from Maryland and Virginia/ It is not 

 intended to state that A. spinosa does not occur in this region; but 

 according to the writer's observations and the collections of the State 

 Survey the common species is A. reticularis. This species is distinguished 

 by its large size, shape, great convexity of dorsal and slight convexity of 

 ventral valve, closely incurved ventral beak, rounded bifurcating plications 

 crossed by concentric striae and lines of growth. In A. spinosa the valves 

 are more nearly equally convex, the radiating plications are much coarser, 

 and fewer, and are crossed by very conspicuous concentric lamellae which 

 give a highly reticulated and nodose appearance to the surface of the shell. 



Length, 18-42 mm. ; width, 20-35 mm. 



Occurrence. — Romney Formation, Hamilton Member. East bank 

 Evitts Creek below Wolfe Mill ; on National Eoad northeast of Cumber- 

 land ; along Flintstone Creek in Gilpin. 



Collections. — Mar^dand Geological Survey; New York State Museum; 

 American Museum of Natural History. 



Family SPIRIFERIDAE 



Genus CYRTINA Davidson 



Cyktina LIAMILTONENSIS Hall 



Plate XVII, Figs. 1-9 



Cyrtia hamiltonensis Hall, 1857, Tenth Rep. N. Y. State Cab. Nat. Hist., p. 166. 

 Cyrtina hamiltonensis Hall, 1867, Pal. N. Y., vol. iv, p. 268, pi. xxvii, figs. 1-4; 



pi. xliv, figs. 26-33, 38-52. 

 Cyrtina hamiltonensis Keyes, 1891, Johns Hopkins Univ. Circ., vol. xi, p. 29. 

 Cyrtina hamiltonensis Hall and Clarke, 1893, Pal. N. Y., vol. viii, pt. ii, p. 46, 



pi. xxviii, figs. 23-33, 43, 45, 46, 53. 

 Cyrtina hamiltonensis Schuchert, 1897, Bull. U. S. Geol. Surv., No. 87, p. 198. 

 Cyrtina hamiltonensis Clarke, 1903, N. Y. State Mus., Bull. 65, p. 224. 

 Cyrtina hamiltonensis Grabau and Shimer, 1909, N. Am. Index Fossils, vol. i, 



p. 313, figs. 393a-c. 



Description. — Shell small and spirifer-like ; hinge-line equal to the 

 greatest width of the shell; proportions of length, breadth and height 



'Johns Hopkins Univ. Circ, vol. xi, 1891, p. 29. 

 ^Bull. U. S. GeoL Surv., No. 87, p. 156. 



