48 
PALAEONTOLOGY OF NEW YORK. 
of the rays (in the specimen figured) have been affected, apparently, by some 
injury received during the life of the animal, which has also produced a 
strong varix of growth. 
Ligamental area 1.5 mm. wide at the beak, whence it diminishes towards 
the extremities of the hinge-line, marked by several flat, longitudinal striae. 
Cartilage-pit broad-triangular, situated under the apex. 
The specimen described is 75 mm. in height, 88 mm. in longitudinal 
diameter, and hinge-line 46 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. 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 Peden 
Tranquebaricus (Gmelin). 
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. 
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. 
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 
