PALEONTOLOGY OF IOWA. 517 



FOSSILS OF THE CHEMUNG GROUP. 



BRACHIOPODA. 

 Chonetes fischeri. 



PLVTE VII. FIG. 1 a, b, c. 



Chonetes fischeri : NORWOOD and PRATTEN, Transactions of the Philadelphia Academy of 

 Natural Sciences., 1854, Vol. iii, p. 25. 



SHELL semielliptical ; hinge line slightly less than the 

 width of the shell. Ventral valve moderately convex, some- 

 what gibbous in the middle, and often nearly flat at the 

 umbo and along the hinge line, scarcely auriculate ; hinge 

 line furnished with from five to seven nearly straight tubu- 

 lar spines on each side of the beak. 



SURFACE marked by fine radiating striae and equally fine 

 concentric striae ; beneath which is a textile appearance, 

 caused by a double set of diagonal lines, which are broader 

 but usually less prominent than the radiating striae. Dorsal 

 valve moderately concave, following the curvature of the 

 opposite valve, covered with close radiating striae. 



This shell can be readily distinguished, even in the condition of casts, by the pe- 

 culiar diagonal lines which give a textile aspect to the whole surface, irrespective of 

 the radiating and concentric striae, which, when entire, partially obscure the marking 

 beneath. Although this character is not mentioned by Messrs. NORWOOD and PRAT- 

 TEN, I can have no doubt of the identity of the species, having collected those de- 

 scribed at the same locality. 



Fig. 1 a. A specimen in sandstone, which preserves no radiating stria). 



Fig. 1 b. A specimen in limestone, which partially preserves the radiating strias. 



Fig. 1 c. Enlargement of the surface, showing the radiating striae and diagonal lines. 



Geological formation and locality. In yellow sandstone of the age of the 

 Chemung group, and in a band of limestone associated with the same rock. 



Productus concentricus (n.s.). 



PLATE VII. FIG. 3. 



SHELL small, semielliptical ; hinge line scarcely so long as 

 the greatest width of the shell. Dorsal valve deeply concave, 



