Helderberg Fok.matiox IX Maryland 43 



Occurrence. — Helderberg Formatiox, Keyser Member. Keys^er, 

 West Virginia. 



Collection. — U. S. National Museum. 



Section ISODONTA 

 Family PECTINIDAE 



Genus AVICULOPECTEN McCoy 

 AVICULOPECTEN TENCILAMELLATUS (Hall) 



Plate LXXVIII, Fig. 4 



Avicula tenuilamellata Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 281, pi. li, 

 figs. 1 and 2, 1861. 



Description.— " ^hell orbicularly subovate: left valve scarcely convex; 

 right valve flat; hinge-line straight, shorter than the greatest width of 

 the shell : anterior wing small, short, acute, separated from the body by a 

 deep narrow sinus, not extending as far forward as the anterior margin of 

 the shell; posterior wing short, broader than the anterior, acute at the 

 extremity, not extending to the line of the posterior margin of the shell. 

 Surface marked by a few unequal concentric wrinkles, and by fine, closely 

 arranged, elevated, subirabricating, lamellose striae, which extend over 

 the wings in like manner. Central portion of the shell marked by faint 

 radiating striae." Hall, 1859. 



This shell is cited by Hall as occurring in the Lower Helderberg rocks 

 of Albany and Schoharie counties, New York. The individual at hand is 

 a badly weathered left valve probably of this species. 



Occurrence. — Helderberg Formatiox, Keyser Member. Keyser, 

 West Virginia. 



Collection.— U. S. National Museum. 



