252 Thirty-fifth Keport ok the State Museum. 



ear, a feature also seen in L. tricostatus, which is the reverse of many 

 species of recent Pectenidse, where the anterior ears are developed 

 beyond the posterior; as in Janira longicauda (d'Orbigny), and 

 Pecten Tranquebaricus (G-melik). This species, although seen in 

 only one valve, is characterized by its peculiar surface markings and 

 outline. 



Formation and locality. Hamilton group, from a bowlder found 

 near Elmira, N. Y. 



Lyriopecteis' tricostatus. 



Avicula tricostata, Vanuxem. Geolog. Surv. N. Y. : Report of Third Dist.,p, 



179, fig. 1. 1843. 

 Lyriopecten tricostatus (Vanuxem), Hall. Pal. N. Y., vol. v, pt. 1. Plates 



and Explanations : PI. 4, fig. 11 ; pi. 7, fig. 26 ; pi. 10, figs. 6-12. Jan., 1883. 



Shells large, transversely and more or less obliquely broad-ovate ; height 

 usually less than the length, the proportions varying with the age of 

 the shell ; young specimens are longitudinally elliptical ; mature 

 specimens are more oblique ; while some abnormal forms show a 

 difference in the direction of the transverse diameter of nearly 45° ; 

 margins full, rounded anteriorly, extended on the postero-basal side, 

 and thence following a nearly straight line to the beak. Valves 

 similar in general outline. Right valve flat or slightly concave- 

 Left valve moderately convex. Hinge-line straight, central, varying 

 from more than one-half the longitudinal diameter in young speci- 

 mens, to less than one-half in mature examples. Beak pointed? 

 depressed, directed forward, situated anterior to the middle of the 

 hinge-line, and not extending as far as the margin of the hinge. 

 Umbonal angle 90°. Anterior ear small, triangular, usually 

 less than half the length of the posterior one ; margin rounded ; 

 extremity obtuse ; byssal sinus broad, rounded, indenting the body 

 of the shell, and shortening the anterior ear. In the right valve 

 the notch is deeper and more angular. Posterior ear large, flat, 

 triangular, marked by a distinct sinus which increases with the 

 age of the shell ; margin above the sinus straight, convex or con- 

 cave ; extremity angular. In young specimens the ears are sub- 

 equal, undefined, and without sinus. In older shells the anterior 

 ear becomes diminished, or appears comparatively smaller ; while the 

 posterior ear is increased in size. 



Surface ornamented by from 20 to 25 strong, rounded, continuous 

 rays, with broad, flat interspaces which show from three to ten 

 smaller radii ; and in well-preserved specimens the entire surface of 

 the shell is marked by fine, regular, sharp, elevated, continuous, 



