1897.] NEW YORK ACADEMY OF SCIENCES. 293 



These small spines are somewhat different in form from any of 

 the group to which the}' belong, being relatively broader toward 

 the base and more slender and acute at the summit, while the 

 body is much compressed. The dorsal prominence is peculiar 

 in its breadth and acute edges. These spines are all quite un- 

 symmetrical, the thin margin which borders the posterior sulcus 

 being much broader on one side than on the other. In size and 

 general form they are not unlike those figured by St. John and 

 Worthen in Vol. YI. of the Geological Survey of Illinois, PI. 18, 

 figs. Y, 8 a and which are erroneously referred to Physonemus 

 gigas, N. & W. The spines before us are, however, more com- 

 pressed than those referred to, are broader at the base and the 

 dorsal prominence is more flattened. B3' comparing the figures 

 now given with those contained in the volume cited, it will be 

 seen that the differences from any form there described are such 

 as to require them to be regarded as forming a distinct species. 



In my notes on Stethacanthus contained in Monograph XVI. 

 of the U. S. Geol. Survey', I have shown that all the spines 

 similar to Physonemus altonensis, St. J. & W., are genericall}^ 

 distinct from Physoriemus, that the surface was never orna- 

 mented with tubercles and that they were certainly spines of the 

 pectoral fins. Both the latter points are proven by the discovery 

 of two spines in the fine argillaceous shale with the fins still at- 

 tached and the surfaces perfectly smooth. 



Formation and locality, Burlington limestone, Burlington, 

 Iowa. Type specimen in the cabinet of Mr. W. F. E. Gurley, 

 Danville, 111. 



ASTEROPTYCHIUS GRACILIS, Ncwb. 



(No figure of this species has been found. — Ed.) 



Spines of small size, straight and extremely slender, about four 

 inches long by one-fifth inch in breadth at base ; buried portion 

 relatively long (one inch in the type specimen) conical in 

 form, regularly and finely striated throughout; ornamented por- 

 tion nearly circular in section, traversed by a few strong, pol- 

 ished ridges, 4 or 5 at base, 2 near summit, separated by striated, 

 depressed bands. On the anterior margin near the base are set 

 several conical tubercles. The posterior face carries two rows 

 of relatively large, conical, subacute denticles which are turned 

 upward, unless at the tip, which is wanting in the type specimen. 



This slender and distinctly marked spine is most like Aster- 

 oplychius St. Ludovici, St. J. & W., described in Vol. VI. of the 

 Report of the Geological Survey of Illinois, p. 437. PI. 16, figs. 

 3 a to 4 g, but it is less curved, more slender, less compressed, has 



