48 PALEONTOLOGY OF NEW YORK. 



of the rays (in the specimen figured) have been affected, apparently, hj some 

 injury received during the life of the animal, which has also produced a 

 strong varix of growth. 



Lisamental area 1.5 mm. wide at the beak, whence it diminishes towards 

 the extremities of the hinge-line, marked by several flat, longitudinal stria'. 

 Cartilage-pit broad-triangular, situated under the apex. 



The specimen described is 75 mm. in height, 88 mm. in longitudinal 

 diameter, and hinge-line 40 mm. The distance between the centres of two 

 of the large rays at the basal margin is about 17 mm. 



The surface markings resemble L. tricostatus, but they are stronger, more 

 rugose, and the rays less numerous; also the shell is not oblique, and the beak 

 is more obtuse and rounded. It differs from L. macrodontus and L. magnificus 

 in its greater convexity, deeper byssal sinus, larger posterior ear, and by its 

 surface characters. This remarkably large and fine species shows conspicu- 

 ously the diminished anterior ear, a feature also seen in L. tricostahis, 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 

 Tranquebaric.us (Gmeijn). 



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. 



Lyriopecten tricostatus. 



PLATE IV, FIG. 11 ; PLATE VII, FIG. 26; AND PLATE X, FIGS. 6-12. 



. I r;<-„Ui trkoxtata, Vandxbm. Geolog. Surv. N. Y. : Report of Thjrd I>ist.. p. 179, tig. 1. 1S43. 

 Lyriopecten tricostatus (Yantxkm), Hall. Pal. N. Y., vol. v. pt. 1. Plates and Explanations: PI. 4. tig. 11 ; 



pi. 7, tig. 26 ; pi. 10. tigs, t; 12. Jan., 1883. 



Shell 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 



