LAMELLIBRANCHIATA 



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, U ; VI, FIGS. 1-9; XXIV, FIG. 7 ; and LXXXJ, FIGS. 13-17. 



Moiwtis princepts, Conrad. Annual Report N. Y. Geolog. Survey, p. 117. 1S38. 

 Avicula parilis, " Proceedings Acad. Nat. Sci. Phila., vol. 8, p. 239, pi. 112, fig. 9. 1842. 



Compare Aviculopecien Sanduskyenxis, 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. 

 Aviculopeeten princeps, (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. 

 Aviculopeeten Sanduskyeiisis, (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 

 1 



