42 
PALEONTOLOGY OF NEW YORK. 
Interior characters not observed, except an indication of a well-defined 
ligamental area. 
The specimen is 45 mm. in height, 48 mm. in length, and the hinge-line 
43 mm. 
This species resembles L. parallelodontus, but differs in the comparatively 
larger and more extended posterior ear and fewer and stronger rays, without 
regular alternation of size. L. orbiculatus is more elongate, with more numerous 
radii and less defined anterior ear. 
The figure is from a gutta percha cast of a mould of the exterior of the shell. 
Formation and locality. In the limestone of the Upper Helderberg group, 
Le Roy, Genesee county, N. Y. 
Lyeiopecten orbiculatus. 
PLATE IV, FIGS. 3-8; and PLATE LXXXII, PIG. 3. 
Avicwla orliiculata, Hall. Geolog. Surv. N. Y.: Rep. Fourth Dist., p. 202. 1843. 
Lyriopecten orbiculatus, Hall. MS., vol. v, pt. 1. 1877. 
“ “ “ Catalogue Amer. Palaeozoic Fossils, S. A. Miller. 1877. 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 4, figs. 3-8. 
Jan., 1883. 
Not Aviculopecten orbicularis, McCoy. Carb. Foss, of Ireland. 1844. 
“ “ orbiculatus, “ “ “ “ “ 
Shell large, orbiculate, becoming wider and oblique with age; length and 
height equal in small and medium individuals; in large specimens the height 
is sometimes one-ninth greater than the longitudinal diameter; basal and 
lateral margins full and regularly rounded. 
Left valve moderately convex; umbonal region ample. Right valve con¬ 
cave, flat or slightly convex over the umbonal region. 
Hinge-line straight, central; length in young shells equal to four-fifths or * 
five-sixths of the longitudinal diameter; and in large specimens the length 
is sometimes not more than one-half the length of the valve. 
Beak obtuse, slightly oblique to the hinge, not rising above it, situated 
anterior to the middle of the hinge-line, and to the centre of the valve. 
Anterior ear of left valve, in small shells, comparatively large, triangular, 
