-\-2 PALAEONTOLOGY OF NEW YORK. 



Interior cliaracttTs not observed, except an indication of a wcll-(lelinc(l 

 lifiainental area. 



The specimen is 4.-3 mm. in heij^ht, 48 mm. in lengtii, and the hiuge-liuc 

 4o mm. 



Thi.s species resembles L. parallelodontus, bnt difl'ers in tlie comparatively 

 larirer and more extended posterior ear and fewer and stronger rays, without 

 rejruhir 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 moidd of the exterior of the shell. 



Formation and locality. In the limestone of the Upper Ileldeilicrg group, 

 Le Roy, Genesee coimty, N. Y. 



Lykiopecten orbiculatus. 



PLATE IV, FIGS. S-8; AND I'LATK I.X.XJXII, FIG. i. 



Amriila orlriciilala. Hall. (Jeolog-. Siirv. N. V. : Kcp. Kouitli Di.-^t., ji. 202. 1S48. 

 LyrUipfcten ivrbicalatus, Hali,. MS., vol. v, pt. 1. 1877. 



" " " Tatalog-ue Anier. Palaeozoic Fossils, S. A. Millkr. lf<77. 



I'jil. N. Y., vol. V, pt. 1; Plates ami Explanations: PI. 4, Hjrs. .3-8. 

 Jan., 1883. 

 Not Arittilnpeiteii orbiadari.i, McCoy. Carb. Fos.o. of Irelaml. IS44. 

 tirh'wulnUis, " " " " " 



Shell large, orbiculate, becoming Avider and (ilili([nc witli iiuc : Icnutli nml 

 height equal in small and nu'diniii individuals; in large specimens the height 

 is sometimes one-ninth greater than the longitmlinal diameter; basal and 

 lateral margins full and regularly rounded. 



Left valve moderately convex; mnbonal region ample. Kight valve con- 

 cave, flat or slightly convex over the umbonal region. 



Ilinge-line straight, central ; length in young shells ecpial to four-fifths or 

 five-sixths of the longitudinal diameter ; and in large specinu us 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 middli' of the hinge-line, and to the centre of the valve. 



Anterior ear of Id't \alve, in small shells, comparatively large, triangular, 



