PRELIMINARY NOTICE 



Part 1. 

 MONOMYAEIA. 



Descriptions of Species. 



GENUS AVICULOPECTEN (McCoy). 

 Section a. 



AVICULOPECTEN PRINCEPS. 



Monotis princeps, Conkad. Annual Report N. T. Geolog. Surv., p. 117.1838. 

 Avicula parilis, Conrad. Proceedings Acad. Nat. Sci. Phila., vol. 8, p. 239, 



pi. 112, fig. 9. 1842. 

 Compare Aviculopecten Sandusky ensis, Meek. Proceedings Acad. Nat. Sci. 



Phila., p. 161. 1871. 

 Compare Avicula parilis, Conrad V Meek. Palaeontology, of Ohio, vol. 1, p. 197. 



1873. 

 Compare A. pecieniformis, Conrad. Jour. Acad. Nat. Sci. Phila., vol. 8, p. 240, 



pi. 12, fig. 14. 1842. 

 Aviculopecten 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. 

 Aviculopecten Sandusky ensis (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 moder- 

 ate 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 the antero-lateral margin with little variation. Beaks 

 obtuse, rounded, anterior to the middle of the hinge. Umbo sub- 



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