LOWER HELDERBERG ROCKS. 
Sjiirlfer perlaiuellosus (n. s.). 
Plate XXVI. Fig. 1 & 2. 
Spirifer rugosa : Hall in Catalogue. 
Shell trigonal or semicircular, more or less extended on the hinge line, 
the extremities varying from obtuse or rounded to extremely inucro- 
nate. Ventral valve arcuate, the beak much extended beyond the 
opposite valve, and incurved at the apex : sinus deep, gradually ex¬ 
panding, and produced in front into a linguiform extension. Dorsal 
valve convex towards the middle, the mesial elevation very prominent, 
and the beak closely incurved against the area, or partially closing the 
foramen of the ventral valve. Area moderately wide, frequently much 
expanded, and becoming linear towards the extremities when the 
shell is much extended. 
Surface marked by four to six strong and abruptly elevated plications 
on each side of the mesial sinus and elevation, concentrically marked 
by strong imbricating lamellm, which are abruptly arched in passing 
over the plications, giving an extreme roughness to the surface. In 
well-preserved specimens, liner longitudinal striae mark the surface of 
these lamellae. In ordinary specimens, the concentric lamellae are more 
closely arranged and more distinctly imbricate towards the margin; 
while near the beaks they are more distant, and are scarcely imbricate. 
This species, in its young state, closely resembles the S. sulcatus of the Niagara 
group; but this shell is more rugose, and the lamellae less arched on the plications, 
which are also less numerous in specimens of the same size. The area, in both 
species, is subject to much variation. 
The form of this species varies mainly in the greater or less extension of the 
cardinal extremities. 
Fig. 1 a-s. Illustrations of gradations of size and differences of form presented by this species. 
Fig. t. Enlargement of surface, showing the concentric lamellae [which are not strong enough 
in the figure] and *the fine longitudinal striae. 
Fig. 2 a, b. Interiors of ventral valves. Fig. 2 c, cl, e. Interiors of dorsal valves. 
Fig. 2 f, g. Cast of the interior, and enlargement of the papillose surface. 
Geological position and locality. In the shaly limestone of the Lower Heidelberg 
group, and rarely in the Pentamerus limestone : Heidelberg mountains; Schoharie, 
Carlisle, Catskill, Hudson, Cherryvalley, etc. 
[ Paleontology III.] 26 
