NATURAL SCIENCES OP PHILADELPHIA. 
411 
and S. W. 1, S. W.£, Sec. 26, Allen. These localities are all in the lower part 
of the Marshall sandstone. 
The variety of this species somewhat resembles C. Michiganensis, Stevens. 
(Sill. Jour. [2] xxv. p. 263), but the spines and ribs are much less numerous, 
not to speak of the alleged direction of the spines in Dr. Stevens’ species. 
Chonetes setigera ? Hall. (Geol. Rep. 4th Dist. N. Y., p. 180; 10th Rep. 
N. Y. Regents, p. 150).—Shell small, semicircular, flattened; hinge line 
slightly less than greatest width ; ventral valve regularly convex, except upon 
the flattened hinge angles; median ridge feeble; hinge with two (perhaps 
three) strong diverging spines each side of the beak; dentigerous plate with 
four tootli-like elevations each side of the beak, slightly elongated in a direc¬ 
tion at right angles with the cardinal spines. Surface marked by about 80 
minute diverging striae, obsolete except near the border, and sometimes one or 
two distinct concentric wrinkles. Dorsal valve slightly concave, striated nearly 
to the beak. 
Length -25 (100) ; breadth *36 (145) convexity of ventral valve *04 (16). 
Locality. —Union, Branch county, in argillaceous shales of the Huron 
group. 
This species differs from the New York specimens of C. setigera in the in¬ 
clination of its spines, and the much greater number of radiating striae. 
Producta, Sowerby. 
Producta concentrica, Hall. (Iowa Greol. Rep., p. 517, pi. vii. fig. 3; 10th 
Rep. N. Y. Reg. p. 180.)—All my -specimens of this species from the southern 
part of the State exhibit, like the Iowa ones, only the inside of the concave 
valve. On the other hand, fragments of a species supposed to be the same, 
from the grindstone quarries at Pt. aux Barques, present only the exterior of 
the convex valve, a circumstance which may throw suspicion on the identifi¬ 
cation of the two sets of forms. 
Myalina, de Koninck. 
Myalina Michiganensis, n. sp.—Shell of medium size, oblique, equivalve, yl/ 
inflated, posteriorly winged, with a straight hinge line. Beaks compressed, ' r 
acute, incurved, and slightly directed forward, but little elevated above the V, u<- 
hinge line ; posterior margin very slightly concave below the extremity of the 
hinge ; thence describing a semi-circle or more to the middle of the anterior 
margin, where a deep incurvation exists, bounded by a small pouch-like ex¬ 
pansion which projects a little anterior to the beaks. Anterior umbonal slope 
somewhat vertical to the shell-plane; the posterior gradual, towards the mar¬ 
gin becoming nearly parallel with the same plane. Hinge furnished in the 
left valve with two small, curved diverging teeth just anterior to the beaks ; 
behind the beaks a narrow ligamental area extends the whole length of the 
hinge ; this area is marked by three longitudinal slightly diverging furrows— 
the outer parallel with the hinge line and co-extensive with it, the middle 
reaching the inner border of the ligamental area at two-thirds the distance 
from the beak to the hinge extremity, the third meeting the same border still 
nearer the beak. Surface marked by irregular, fine incremental lines, some of 
which are more deeply impressed. 
Greatest dimension of shell from beak to ventral margin along the umbonal 
slope 1*25 (100) ; angle included between this line and hinge line 50° ; diame¬ 
ter of shell from umbo to umbo *78 (62); length of hinge *67 (53) ; angle 
formed by hinge line and posterior margin 112°—120° ; projection of shell an¬ 
terior to the beaks, ’19 (15). 
Localities. —Marshall (abundant), Moscow; This interesting species resem¬ 
bles M. virgula, de Kon. (An. Foss. 127, pi. vi. 3). It is, however, less oblique, 
less indented on the posterior border, and more prominent in front of the 
umbo. 
1862 .] 
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