SPIRIFER2E OF THE HAMILTON GROUP. 
281 
This species may be compared with S. segmenta of the Corniferous limestone; 
but I have not been able to identify the two as a single species. 
Geological formation and localities. This species occurs in the Hamilton group 
at Geneseo and York in Livingston county, and at Covington in Genesee county. 
Spirifera macronota. 
PLATE XXXYIII A. 
Delthyris macronota : Hall, Geol. Report Fourth District New-York, p. 206, f. 5. 1843. 
Spirifer macronotus : Hall in Catalogue in Report on State Cabinet. 1859. 
Shell transverse, subtrianguldr or broadly semielliptical; hinge-line 
much extended, extremities often mucronate: valves unequal in depth; 
area large ; surface plicate. 
Ventral valve elevated at the beak, abruptly sloping to the front and 
lateral margins, with but little convexity: slope of the cardinal border 
very regular to near the extremities. Area one-third as high as long; 
more usually straight or very slightly arcuate, and longitudinally 
striate : fissure about twice as high as wide, reaching to the apex of 
the valve; beak minute. Mesial sinus rapidly widening, shallow, flat¬ 
tened at bottom, with margins subangular especially in the upper part. 
Dorsal valve varying from depressed-convex to gibbous, most convex 
above the middle; lateral extremities often inflected; beak incurved, 
not prominent: area linear. Mesial fold well marked, usually flattened 
on the top, sometimes strongly rounded. 
Surface marked by from twenty-five to thirty-five slender simple ra¬ 
diating plication! on each side of the fold and sinus ; these are either 
flattened or rounded : three or four only on each side reach to the 
beak, while the remainder are lost on the margins of the area. The 
valves are crossed by numerous strong concentric imbricatingTines of 
