Maryland Geological Survey 265 



shows well the alternation and intercalation of the rays together with their 

 faint appearance on the ears. 



Length, of medium specimen, about 30 mm. ; height, about 45 mm. 



Occurrence. — Eomnky Formation, Hamilton Member. B. & 0. 

 E. E. cut at 21st Bridge ( ?) ; Williams Eoad \ mile northeast of Queen 

 City Hotel, Cumberland; McCoys Ferry; southwest of McCoys Ferry; on 

 Hancock-Harrisonville Eoad about 2 miles north of Hancock; west of 

 iron bridge over Town Creek northeast of Oldtown ( ?). 



Collections. — Maryland Geological Survey; New York State Museum; 

 American Museum of Natural History. 



AVICULOPECTEN EQUILATERA (Hall) 



Plate XXXII, Figs. 3, 4 



Avicula equilatera Hall, 1843, Nat. Hist. N. Y. Geology, vol. iv, p. 180, text fig. 



7; p. 181, table illus. 39, fig. 7. 

 Avicula equilatera Owen and Hall, 1847, Amer. Jour. Sci., 2d ser., vol. ill, p. 



59, fig. 7 in text. 

 Aviculopecten equilatera Hall, 1859, 12tli Rept. N. Y. State Cab. Nat. Hist., 



p. 89. 

 Avicula equilatera Lincklaen, 18G1, 14th Rept. N. Y. State Cab. Nat. Hist., pi. 



xii, fig. 7. 

 Aviculopecten equilaterus Lesley, 1889, Geol. Survey Penn., Rept. P4, p. 74, 1 



text fig. 

 Aviculopecten ? equilatera Whitfield, 1891, Annals N. Y. Acad. Sci., vol. v, 



p. 551, pi. xi, fig. 16. 

 Aviculopecten ? equilatera Whitfield, 1893, Geol. Survey Ohio, Paleontology, 



vol. vii, p. 445, fig. 16. 

 Aviculopecten equilatera Kindle, Bull. U. S. Geol. Surv., No. 508, p. 93, pi. 



viii, figs. 2, 3, 1912. 



Description. — Shell small and slightly oblique, depressed convex. 

 Hinge-line straight, equal to greatest length of shell. Beak nearly central 

 on hinge-line. Anterior cardinal angle apparently mucronate ; margin of 

 shell below the cardinal line slightly sinuate and gently rounded to the 

 posterior margin, which is nearly straight but is directed slightly back- 

 ward in descending from the hinge-line to the rounded posterior margin. 

 Surface covered wdth 15 to 20 strong rounded plications, which are crossed 

 by finer concentric undulations. 



