ORISKANY SANDSTONE. 
425 
Spirifei* aicnosus-. 
Plate XCVIII. Fig. 1 - 8 ; Plate XOIX. Fig. 1 - 10 ; and Plate C. Fig. 1-8. 
Delthyris arenosa : Conrad, Annual Report on the Palaeontology of New-York, 1839, p. 65. 
D. — Vanuxem, Report on the Third Geological District, 1843, p. 123, f. 1. 
D. — Mather, Report on the First Geological District, 1843, p.342, f. 1. 
D — Hall, Report on the Fourth Geological District, 1843, p. 148, f. 1. 
Shell, in the young state, semielliptical, with the beak a little elevated 
above the hinge-line ; the old shell becoming ventricose, and the beak 
much elevated above the hinge-line, having a somewhat semioval form. 
The proportions vary from length and width equal, to width one-third 
greater than the length. Cardinal angles sometimes produced in acute 
terminations, but usually rounded, particularly in old shells. 
Ventral valve very regularly convex, the greatest convexity about one- 
third the distance below the beak. The cardinal angles, when produced, 
are a little flattened. The mesial sinus is very shallow, being often little 
more than a flattening of the surface along that part of the shell. The 
umbo is broad, and the beak a little incurved over the area. Area in 
young shells narrow, and in old shells proportionally wider, and ex¬ 
tending to the cardinal extremities : the foramen is wide, and, in old 
shells, partially closed above. The dental lamellae are strong; the 
extremities, rising above the cardinal line and bending backwards 
beneath the area, are widely divergent as they extend from the beak 
downwards. The muscular impressions are large, and very strongly 
and beautifully marked. 
Dorsal valve of the same form as the ventral; its greatest convexity in 
the middle, with a very narrow cardinal area, above which the beak is 
slightly incurved. Mesial elevation very moderate, and sometimes 
scarcely defined. 
Surface marked by regular simple rounded or sometimes subangular 
plications, of which there are from ten to twenty on each side of the 
mesial fold and sinus. The mesial sinus is simple at the apex; but a 
[ Paleontology III.] 54 
