410 PROCEEDINGS OF THE ACADEMY OF 



valve. 0. Vanuxemi is described from the shales and shaly sandstones of the 

 Hamilton group of New York and Iowa, the lithographic limestones of Mis- 

 souri, and from the soft sandstones in Eastern Ohio, regarded as Chemung by- 

 Prof. Hall. 



Okthis crenistria ? Phillips. (Pal. Foss. Corn. &c, p. 66, pi. 27, fig. 113). 

 Hinge line equalling greatest width of shell; ventral valve semi-elliptic with shal- 

 low constrictions beneath the cardinal extremities ; flat, with an umbonal ele- 

 vation beginning about the middle and rising to a beak which overlooks a large 

 triangular area inclined at an angle of 45 with the shell-plane ; dental plate3 

 strong, each equalling one-fourth the hinge length, forming with each other an 

 angle of about 60. Occlusor scars reaching nearly the middle of the shell, 

 closely contiguous, leaving together a ligulate anteriorly acute depression upon 

 the cast. Surface covered by fine radiating stria?, interrupted by distinct or 

 obscure concentric wrinkles. In one specimen supposed to belong here, the 

 surface is covered by a set of sharply-cut, twice-dichotomizing striae the 

 second set reaching half way, and the third one-third the distance to the beak. 

 Dorsal valve hemispherically convex with sharp stria? and concentric wrinkles, 

 like the ventral. 



Length of shell 1-27 (100) ; length of hinge line 1-37 (107) ; length of den- 

 tal plates -32(25). 



Locality. Light-house, Pt. aux Barques. 



I can make no distinction between this species and that described by Phil- 

 lips, from South Devon. The beak, however, seems to be perfectly symmetri- 

 cal, and in this it differs from Streptorhynchus robusta, Hall, sp., from the coal 

 measures of Iowa, as well as from the Punjab examples of Davidson (Quar. 

 Jour. Geol. Soc. Lond., xviii. p. 30), who identifies the Devon, Iowa and Pun- 

 jab forms. The Michigan forms differ from all the others in the rugose ex- 

 terior, giving it sometimes the aspect of Strophomena rugosa ; but as they at the 

 same time differ among themselves, I am not disposed to hesitate in the iden- 

 tification. 



Orthis Iowensis ? Hall. (Io. Rep., 488, pi. 2, fig. 4.)- Some casts in my 

 possession resemble those of the above species. Ventral valve nearly circu- 

 lar, regularly convex, with deep pit in the beak between the dental plates, 

 which in the cast produces a conical projection. Middle region of cast with 

 three faint rounded ridges radiating from the beak to the anterior margin. 



Lo.ality. Light house, Pt. aux Barques. 



Chonetes, Fischer. 



Chonetes pulchella, n. sp. Shell small, nearly semi-circular ; hinge al- 

 most equalling the greatest width, rectangular at the extremities, furnished 

 with two or three stout hollow spines on each side of the beak, one projecting 

 from the hinge extremity, and diverging at an angle of about 22 with the 

 hinge line the second half way to the beak and diverging at an angle of 45, 

 each of these spines having a length equal to half the hinge line. Ventral 

 valve, exclusive of the flattened hinge angles, spherically convex ; internal me- 

 dian ridge extending to the middle of the valve. Surface with about 54 feeble, 

 rounded ribs, often nearly obsolete on the hinge angles ; these are crossed by 

 numerous microscopic, concentric stria? ; the grooves beneath the ribs are 

 acute and bear a few spinous projections near the shell margin. Dorsal valve 

 nearly flat, generally a little concave near the margin, marked like its fellow 

 with radiating stria?, and often a few concentric folds. Area very narrow, 

 equally excavated in the two valves. Some specimens exhibit a shorter hinge 

 line, and a flatter ventral valve, elevated only in the umbonal region, with a 

 beak projecting slightly beyond the hinge. 



Length -30 (100) ; breadth -38 (126) ; convexity of ventral valve -07 (23). 



Localities. Hillsdale county at Moscow, N. W. \, N. W. , Sec. 4, Jefferson, 



[Sept, 



