LAMELLIBRANCHIATA. 299 



the sinus is marked by strong, elevated, radiating strige, which dominate 

 the concentric striae. The test is raised into a crest along the umbonal 

 ridge, especially in the posterior half of its length. 



Anterior muscular impression large and deep, situated close to the anterior 

 margin, truncated posteriorly by a strong ridge or clavicle. Pallial line 

 parallel to and near the basal margin, appearing as a shallow groove, recurv- 

 ing near the post-basal extremity and terminating in a broad, muscular 

 impression, the anterior margin of which is near the center of the length of 

 the shell. 



A specimen of medium size has a length of 54 mm., and a height of 23 

 mm. A somewhat smaller individual measures 50 mm. in length and 20 

 mm. in height. 



This species is very closely allied to G. perangulaia of the Schoharie grit, and 

 it is possible that they are identical. In the specimen fig. 3 of plate xl, the 

 hinge-line is shorter than in specimens of G. perangulata, but the compara- 

 tive length of the hinge-line appears to be variable in the two species. Other 

 differences are pointed out under the description of that species. 



Formation and localities. In the shales of the Hamilton group, on the shores 

 of Cayuga and Skaneateles lakes, at Delphi and Pratt's falls, Onondaga 

 county, N. Y. 



GONIOPHORA GlAUCUS. 



PLATE XLm, FIG. 16; AND PLATE XLIV, FIGS. 10-17. 



SanguinolUes Olaueus, Hall. Prelim. Notice Lamellibranchiata, 2, p. 38. 1870. 

 Goniophora glabra, Hall (in eiTor). S. A. Miller. Cat. Amer. Pal. Foss., p. 192. 1877. 



.• " " Pal. N. y., vol. V, pt. 1. Plates and Explanations : PI. 44, figs. 9-17. 1883. 



Shell large, trapezoidal ; length once and a half greater than the height ; basal 

 margin gently curved, sometimes scarcely sinuate anterior to the middle ; 

 posterior margin obliquely truncate ; cardinal line nearly straight or slightly 

 oblique ; anterior end declining from the beaks and abruptly rounded below. 

 Valves moderately convex below, sometimes becoming gibbous in the 

 umbonal region. 



