SPIRIFER^ OF THE HAMILTON GROUP. 231 



c> 



Spibifeba xsavsTA.. 



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 XXXVIII A. 



DellhyrU macronota : Hah, Geol. Report Fourth District New-Torlc, p. 206, f. 5. 1843. 

 Spirifer macronolus ; Hall in Catalogue in Report on State Cabinet. 1859. 



Shell transverse, subtriangular 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. Mesia«l fold well marked, usually flattened 

 on the top, sometimes strongly rounded. 



Surface marked by from twenty -five to thirty-fi^e slender simple ra- 

 diating plications 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 imbricating lines of 



