776 Report oF THE State GEOLOGIST. 
or flanges, beginning at the hinge-line, having a slightly sinuous 
curve and terminating before traversing much more than one- 
third the length of the valve; occasionally there is a second of 
these ridges on each side. 
The muscular impressions of the valves are essentially as in 
Meeisretta. The hinge-plate has a peculiar structure; it arises 
vertically from the bottom of the valve, presenting an erect, con. 
cave anterior face, which is traversed by a faint median ridge 
continuous with the septum of the valve. The posterior portion 
of the upper surface of this plate bears a deep circular or 
crescentic concavity, most sharply defined on its anterior edge 
where it is bounded by the somewhat recurved vertical wall. On 
the lateral portions of the upper face of the anterior wall lie the 
elongate crural bases which are continued into short, straight 
crura, standing at an angle of about forty five degrees to the 
plane of the horizontal face of the plate. The spiral cones are 
as in Mrrisre.ta, their curvature conforming to the peculiarly 
contracted interior cavity of the shell. Precise nature of the 
jugum not known. 
Type, Pentagonia wnisulcata, Conrad (sp.). 
Distribution. Devonian (Upper Helderberg and Hamilton 
groups). 
Camarospira, Hall. 1893. 
(Plate 33, figs. 20-23.) 
Shells essentially meristelloid in external and _ internal 
characters. The important difference from allied genera lies in 
the fact that the dental plates of the pedicle-valve, instead of 
resting upon the bottom of the valve, are more strongly conver- 
gent than in Mzrisra, Mrrisreta, etc., uniting before they reach 
the internal surface of the valve, thus restricting the impression 
of the pedicle-muscle to a distinct chamber or spondylium, which 
is supported by a low median septum. In the typical species 
this chamber has the same extent as the deep pedicle-cavity in 
Merisrexxa, that is, about one-fourth the length of the valve, 
while the septum extends for a short distance beyond its anterior 
margin, dividing the scars of the adductor and diductor 
impressions. In this respect the internal structure of this valve 
is similar to that of the corresponding valve of Penramervs. 
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