242 PALEOZOIC PALEONTOLOGY. 
valves are rather strongly convex, the greatest depth being near the 
centre. 4 
The dimensions of the type specimen, a right valve, are: length, 24 
mm.; height, 18 mm.; convexity, 5 mm. 
Remarks.—The hinge characters of this shell are not preserved, so 
that its generic reference is somewhat uncertain. The surface char- 
acters are also obliterated,-but the shell is believed to be nearly smooth 
or to be marked only by lines of growth. 
NUCULA? sp. undet. 
Plate XXII., Fig. 5. 
Description.—Shell small, subovate in outline, obliquely truncated 
posteriorly, regularly convex. The beak is prominent, situated a little 
in front of the middle of the shell. Surface marked by fine, concentric 
lines of growth. ; 
The dimensions of the most perfect valve are: length, 14.5 mm.; 
height, 10 mm., and convexity, 3.5 mm. 
Remarks.—The hinge characters of this species have not been ob- 
served, but the shell itself has the general form and appearance of 
many Nuculoid shells, so that it is referred provisionally to the genus 
Nucula. 
PTERINEA EMACERATA (Con.). 
Plate XXIIL., Fig. 4. 
1842. Avicula emacerata Conrad, Jour. Acad. Nat. Sci. Phil., vol. 
WILT, p. 241, pl 12, fie. Lo. 
1852. Avicula emacerata Hall, Pal. N. Y., vol. IL., p. 83, pl. 27, fig. 
1 a—b, p. 282, pl. 59, fig. 1 a-e. 
Description.—Shell oblique and, apart from the posterior wing, sub- 
ovate in outline. Left valve convex, with straight hinge-line. The 
posterior wing extended a little further than the posterior margin 
and separated from the body of the shell by a concave sinus; termi- 
nating in an acute point, below which the margin of the shell is 
sinuate. Beak nearly terminal, slightly elevated above the hinge- 
