LAMELLIBRANCHIATA 
OF THE 
UPPER HELDERBERG, HAMILTON, PORTAGE AND CHEMUNG GROUPS. 
DESCRIPTIONS OF SPECIES. 
AVICULOPECTEN, McCoy. 
Section a. 
Aviculopecten princeps. 
PLATES I, FIGS. 10, 11; V, FIGS. 18,19, 23, 24 ; YI, FIGS. 1-9; XXIV, FIG. 7 ; AND LXXXI, FIGS. 13-17. 
Monotis princeps, Conrad. Annual Report N. Y. Geolog-. Survey, p. 117. 1838. 
Avicula parilis, “ Proceedings Acad. Nat. Sci. Phila., vol. 8, p. 239, pi. 112, fig. 9. 1842. 
Compare Aviculopecten Sanduskyensis, Meek. Proceedings Acad. Nat. Sci. Phila., p. 161. 1871. 
Avicula parilis, Conrad ? Meek. Palaeontology of Ohio, vol. 1, p. 197. 1873. 
“ A. pecteniformis, Conrad. Jour. Acad. Nat. Sci. Phila., vol. 8, p. 240, pi. 12, fig. 14. 1842. 
Aviculopecten pinnceps, (Conrad) Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: Pi. 5, figs. 
18, 19, 23, 24; pi. 24, fig. 7. Jan., 1883. 
Aviculopecten Sanduskyensis, (Meek) Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 1, figs. 
10, 11. Jan., 1883. 
Shell large, obliquely broad-ovate; axis inclined more than 60° to the hinge¬ 
line; length and height nearly equal, varying within moderate limits; 
anterior margin convex; the convexity increasing to the middle of the 
postero-lateral side, thence truncated and extending in a straight line to 
the beak, making an angle of from 30° to 40° with the hinge-line. Valves 
depressed; left valve regularly convex; right valve nearly flat, or very 
moderately convex. 
Hinge-line straight, having a length of from two-thirds to more than 
three-fourths the length of the shell, and extending anteriorly as far as 
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