NATURAL SCIENCES OP PHILADELPHIA. 411 



and S. W. |, 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 setigeka ? 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 tooth-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. 



Pkoddcta, Sowerby. 



Pkoducta concentrica, Hall. (Iowa Geol. 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, 

 inflated, posteriorly winged, with a straight hinge line. Beaks compressed, 

 acute, incurved, and slightly directed forward, but little elevated above the 

 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 '61 (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, le3S oblique, 

 less indented on the posterior border, and more prominent in front of the 

 umbo. 



1862.] 



