206 
PALEONTOLOGY OF NEW-YORK. 
depressed along the centre; the beak projecting a little above the 
hinge-line, and with a narrow area gently incurved. 
The surface is marked by from eight to ten simple and somewhat 
abruptly elevated plications on each side of the mesial fold and sinus : 
these are crossed by strong lamellose imbricating lines of growth, which 
give a varicose character to the surface, and where the shell is exfolia¬ 
ted the plications are nodose. 
In some specimens, distinct fine radiating striae can be observed. 
There is often a retral curving of the concentric striae in the centre of 
the mesial sinus, and sometimes a slight elevation along that line. 
The original specimens of this species were obtained from a western locality ; 
but there are forms in Western New-York, which, though differing slightly from 
the originals, seem nevertheless referable to the same species. 
,In comparing this with other generally similar forms, I remarked in my original 
description that this species differs from 8. euruteines of Owen, in being smaller 
and more transverse, with more angular plications and stronger concentric lines of 
growth ; also, in the greater prominence of the two plications bounding the 
sinus, as well as the abrupt and angular mesial fold. It differs from 8. segmenta in 
its fewer and more rugose plications, as well as in the more abrupt mesial sinus, 
and in the inclination of the area. 
The figures 1-4, Plate 31, are of typical forms of this species, of which I have 
more than a dozen individuals before me, all preserving the same characters with¬ 
out material variation. 
Geological formation and locality . In limestone of the age of the Upper Hel- 
derberg limestone at Charleston landing, Indiana; at Williamsville, etc., New- 
York. 
Spirifera varicosa, var. 
PLATE XXXI. 
Shell having the general characters of S. varicosa, but larger and more 
gibbous; area higher, but similarly arcuate in the upper part. There 
are ten or more plications on each side, which are rugose from strong 
imbricating lamellae, and become somewhat nodose on partial or entire 
exfoliation. Unfortunately only a few specimens of this variety have 
been seen in New-York. 
