218 
PALAEONTOLOGY OF NEW-YORK. 
and the teeth-sockets are large, while the bases of the crura are often 
distinctly seen. The interior surface is usually papillose. 
Geological formation and localities. This species begins its existence in the 
Marcellus shale (figure 3); and is abundant everywhere in the Hamilton group, 
sometimes constituting thin layers to the exclusion of every other fossil. In the 
eastern part of the State, in the arenaceous shales of this group, it occurs in the 
form of casts ; and this is its usual condition in Schoharie, Otsego and Madison 
counties, while from Cayuga lake westward it retains the shell. In some places in 
Canada West it is found to be the prevailing fossil, while scarcely any other 
Spirifer occurs in the same association. I have received specimens of this shell, 
said to have been found near the Falls of the Maumee river. It occurs likewise 
in Maryland and Virginia. 
In the Drift of Ohio, Indiana and Illinois, this species occurs more frequently 
perhaps than any other fossil. 
The Spirifer a bimesialis (Geol. Report of Iowa, page 507, plate 4, figure 6 ) is 
closely allied to S. vmcronata , differing mainly in the much wider area and more 
elevated beak of the ventral valve. The S. subattenuata and S. inutilis of the same 
volume (pages 504 and 505, plate 4, figures 3 and 4) have similar external cha¬ 
racters, with a shorter hinge-line and higher area than S. bimesialis. These two 
species are represented in form and proportions (except the extreme narrow area) 
by S. mvcronata, Plate 33, figures 19, 20 and 21 of this volume. 
Spirifera twllia (n. s.). 
PLATE XXXV. 
Shell gibbous, subelliptical; length and width about as two to three, or 
as three to four : hinge-line equalling or greater than the width of 
the shell; cardinal extremities truncate or auriculate. 
Ventral valve gibbous, the greatest convexity above the middle of the 
shell, regularly arcuate from beak to base, curving abruptly to the 
sides and a little flattened at the cardinal extremities; beak strongly 
incurved : sinus sharply defined quite to the apex, not deep, rounded 
in the bottom. Area high, flat in the lower part and extending to the 
hinge-extremities, concave in the upper part. 
