250 PALEONTOLOGY OF NEW YORK. 



iiini. ; the approximate length is 70 mm. and 88 mm., respectively. Another 

 specimen lias a length of 77 nun., and a height of 90 mm. A larger speci- 

 men has a length of DO nun., and a height of 100 mm. 



The specimens of- this species occur in the softer shales of the Hamilton 

 group, and it is possible that long maceration has had some influence in oblite- 

 rating the radii; but L. macroptcra, with its more convex form, and marked by 

 its characteristic radii, occurs in the same localities. Although not entirely 

 satisfied in regard to its specific distinction, it may be convenient to separate 

 this at least as a varietal form. 



Formation and localities. In the Hamilton group, at Hamilton, Madison county, 

 at Delphi, Onondaga county : and on the shore of Cayuga lake, N. Y. 



LlMOPTERA CURVATA. 

 PLATE XXVIII, FIGS. 1-3. 



Limoptera curcata, llin. Prelim. Notice, Lam. Shells, etc., part -. p. IS. Dec, 1869. 



Pal. N. Y., vol. v,pt. 1. Plates ami Explanations : PI. 28. figs. 1-3. Jan.. 1863. 



Shell large, sub-rhomboid-ovate in outline; body broadly ovate, arcuate, 

 expanded on the antero-basal margin. 



Valves very unequal. Left valve very gibbous in the middle and umbonal 

 region. Right valve depressed-convex below, becoming somewhat gibbous 

 on the umbo. Left valve, with the beak, very prominent and incurved ; 

 beak of right valve rising but little above the hinge-line. 



Test thick, marked by strong rounded radii with intermediate finer lines 

 which become obsolete on the lower part of the valve. The radii are crossed 

 by fine, closely arranged stride of growth, which at intervals are crowded and 

 lamellose, especially toward the margin of the valve. 



The internal cast shows the anterior muscular impression situated at the 

 extremity of the rostral cavity, from which the palli.al line, marked by a 

 row of strong pustules, extends nearly parallel to the anterior margin for 

 more than one-third the length of the valve ; thence broadly curving, it 

 extends below the middle of the valve, and recurves into a large sub-circular 



