1897.] NEW YORK ACADEMY OF SCIENCES. 291 



Formation and locality, St. Louis Beds, Salem, Indiana. 

 Types in the cabinet of Mr. Gurle}'. 



Ctenacanthus depressus, n. sp. 

 PI. XXII., fig. 6. 



Spines eight inches or more in length by one inch in breadth, 

 moderately compressed, gently curved backward, posterior face 

 flattened, sides marked with about thirty longitudinal ridges, 

 simple except just at the base where they are forked, subequal 

 except near the posterior margin where they are finer; base 

 smooth or longitudinally striated, line of demarcation between 

 base and ornamented portion extremely oblique, the plain sur- 

 face reaching to the upper third of the length of the spine. 

 This shows that the spine was set in the back at a very low angle 

 and, as a necessary consequence, the posterior opening reaches 

 to and beyond the middle. The tuberculation of the ornamented 

 surface is inconspicuous ; along the anterior border the ridges 

 are set with closely approximated simple and plain tubercles ; 

 on the sides the longitudinal ribs are nearl}' or quite smooth. 



The nearest approach to this spine in form and structure 

 among described species is perhaps Ctenacanthus Buttersi, St. 

 J. & W. (Report of the Geol. Surv., of 111., Yol. VII., p. 240, PI. 

 XXII., fig. 2), but it is very much larger than that species, oc- 

 curs at a different horizon and shows nothing of the curvature 

 of the ribs as they approach the smooth base. Hence it is 

 specifically quite distinct, but the general form of the two 

 species must have been similar and they were alike in being in- 

 clined at a very low angle so that the line of insertion runs far 

 up toward the point. 



Formation and locality, Kinderhook group, Le Grande, Iowa. 

 Type in the cabinet of Mr. William F.E. Gurley, Danville, 111. 



Stethacanthus productus, n. sp. 

 PI. XXIII., figs. 1-2. 



Pectoral spines of large size, eight inches or more in length by 

 two and one-half inches in breadth at base and one and a-quarter 

 inches in thickness, dorsal margin gently curved, dorsal tuber- 

 osity relatively low and narrow, section near summit triangular. 



Several large spines of Stethacanthus are contained in the col- 

 lection of Mr. Gurley. They are, as is so common in the spines 

 of this genus, quite imperfect and yet enough is shown of their 

 form to indicate that they are distinct from the allied large 

 species, S. altonensis and S. tumidus. From the former species 



