264 
PALAEONTOLOGY OF NEW-YORK. 
Position and locality. This species occurs in the limestone of the Niagara group, in its 
eastern extension into Oneida county. The only place I have been able to find it, is at the 
locality cited by Mr. Vanuxem, on the banks of the creek a short distance west of Yernon 
centre. At this place the shells appear upon the surface of the thin layers of limestone, and 
I have been unable to obtain any perfect specimens. 
625. 8. SPIRIFER NIAGARENSIS. 
Pl. LIV. Fig. 5 a-t. 
Delthyris niagarensis. Conrad, Jour. Acad. Nat. Science, 1842, Vol. viii, p. 261. 
— — Hall, Geol. Rep. _4th District, 1843, pag. 105, fig. 1. 
Semioval or semicircular, convex or moderately gibbous in the centre, and compressed to¬ 
wards the sides; valves nearly equally convex; dorsal valve having the beak elevated and 
incurved over the area; area medium width ; hinge-line usually shorter than (rarely extended 
beyond) the width of the shell, with the extremities rounded. Surface marked by twenty to 
thirty rounded, depressed plications (in young shells not more than ten or twelve), longi¬ 
tudinally striated by fine equal striae, which are equally conspicuous on the mesial sinus and 
elevation. 
This shell is typical of the Niagara group, and is always readily recognized by its rounded 
plications, which are evenly striated in a longitudinal direction. There is usually a stronger 
line in the depression between the plications. The surface is similarly striated to the margins, 
but the plications gradually die out towards the cardinal extremities. The area in perfect shells 
is of medium width, but usually appears as if very narrow, and the valves nearly closed, from 
compression. From its large size, it is rarely found in a good state of preservation, and the 
valves are often distorted and compressed, giving an outline very different from the natural 
form. Although having a wide horizontal range, its vertical range is extremely limited, oc¬ 
curring in considerable numbers only through a very limited thickness, of the shale, and rarely 
in the limestone above. 
Fig. 5 a , b. Ventral and dorsal views of a young specimen, which has only about five or six 
defined plications on each side of the mesial fold and sinus. 
Fig. 5 c. Front view of the same. 
Fig. 5 d. Profile view of another more gibbous specimen. 
Fig. 5 e, f, g. Ventral, front and profile views of a well preserved specimen, which has about 
eight defined plications on each side of the mesial sinus and fold. 
Fig. 5 k, i. Ventral and profile views of a well preserved specimen, of the ordinary size of this 
species. 
Fig. 5 Jc. A flattened dorsal valve of about the same size as the preceding specimen, showing 
the change in form produced by compression. 
Fig. 5 1. A flattened ventral valve of a specimen somewhat larger than the preceding. This 
condition of specimens is a very common one in the shale : indeed the perfect form 
is the exception. 
