PALAEONTOLOGY OF NEW-YORK. 
Spirifer macropleurus, 
Plate XXYII. Fig. 1 a-p; and Plate XXYIII. Fig. 8 a - d. 
* 
Delthyris macropleura : Conrad, An. Report on Palaeontology of New-York, 1840, p. 217. 
— — Vanuxem, Rep. on Geology Third District New-York; 1843, pa. 120, f. 1. 
— — Matoer, Rep. on Geology First District New-York, 1843, pa. 343, f. 1. 
Shell large, varying from semielliptical to semicircular or transversely 
elliptical, ventricose : valves nearly equally convex; hinge line often 
scarcely equalling the greatest width of the shell. Area narrow. Fo¬ 
ramen large. Ventral valve with a broad deep curved sinus and three 
strong rounded plications on each side : beak moderately elevated 
above the opposite, and abruptly incurved. Dorsal valve with a broad 
rounded mesial fold and two strong rounded plications, with sometimes 
a third one on each side. 
Surface marked by fine closely arranged radiating striae, which are 
crossed by finer concentric ones (the latter rarely visible). 
This species, in its general characters, is a representative of the type of a group 
of which S. radiatus and S. niagarensis are the earliest known forms; and is the only 
one of this character that I have seen in the Lower Helderberg group in New-York. 
PLATE XXVII. 
Fig. 1 a. A young shell in which the plications are hut faintly developed. 
Fig. 1 b, c. Dorsal and profile views of a specimen of medium size. 
Fig. 1 d & h. Front and cardinal views of the same. 
Fig. 1 e,f, g. Dorsal, front and cardinal views of a very symmetrical form of medium size. 
Fig. 1 k. Ventral view of a larger individual. 
Fig. 1 l. Cast which is somewhat crushed from the base. 
Fig. 1 m, n. Interior of the ventral valve, and cast of the same. 
Fig. 1 o. Part of the exterior of a slightly weathered specimen, showing the extremity of 
the spire. 
Fig. 1 p. Enlargement of the radiating strise as seen under a lens upon the surface of ordi¬ 
nary specimens. 
PLATE XXVIII. 
Fig. 8 a, b, c. Casts of the ventral valve showing some variety in the forms of the muscular 
impressions. , 
Fig. 8 d. Enlargement of the surface striae, taken from a mould of the exterior in the shaly 
limestone, where the shell has decomposed. 
[ This character is rarely well preserved on the surface of the fossil.] 
Geological position, and locality. In the shaly limestone of the Lower Helderberg 
group : Helderberg mountains ; Schoharie, Carlisle, Catskill, Hudson ; Penn¬ 
sylvania, Maryland and Tennessee. 
