914 
PALAEONTOLOGY OF NEW-YORK. 
where the surface is partially or entirely exfoliated, the bifurcating cha¬ 
racter of the striae is not observed; and in one specimen, they appear 
to have been nearly simple throughout. 
The plications are crossed by fine imbricating lamellose striae, which 
are abruptly arched backwards. 
A cast of the ventral valve shows a large oval muscular area, which 
is deeply divided by a rounded median crest, and strongly striated on 
the lateral portions. 
After examining all the collections that have been made, I am unable to point 
out any specific difference between the specimens originally described by me as 
8. divaricatus , and those subsequently described as 8. veniistus, from the Hamil¬ 
ton group. The specimens then before me were in the condition of the one figured 
on plate 32 figure 1; while the Hamilton specimens, illustrated in figures 2-6, 
offered at first view very little similarity with those of the limestone, and were 
regarded as a distinct species. Other specimens from the limestone have a nearer 
approach to those of the Hamilton shales. 
This shell, in its proper form and proportions, is one of the finest Spirifers in 
the whole series, and is readily distinguished from all others by the bifurcating 
plications and sharp zigzag concentric striae. The largest specimen seen has a 
width of nearly three inches with a length of two inches, and a depth of one inch 
and an eighth. 
Geological formations and localities . In the Corniferous limestone at Scho¬ 
harie; at Stafford in Genesee county; at Williamsville and Clarence in Erie 
county. In the Hamilton group, at York, Livingston county. I have seen a frag¬ 
ment of this species from the limestone near Port Colborne, Canada West. 
Spirifera fimbriata. 
PLATE XXXIII. 
Delthyris fimbriata : Conrad, Jour. Acad. Nat. Sciences Philadelphia, Vol. viii, p. 263. 1842. 
Spirifer fimbriata : Conrad ; Billings in Canadian Journal, p.'259. 1861. 
Shell transversely subelliptical, gibbous : hinge-line less than the width 
of the shell; cardinal extremities rounded. 
Ventral valve gibbous in the upper half, regularly curving to the front 
and sides; sinus well defined, usually shallow and rounded, sometimes 
deep and angular, and much produced in front; beak small and 
incurved over the area, which is high and concave and extending 
