288 TRANSACTIONS OF THE [mAR. 15, 



tubercles which are beautifully sculptured and are, toward the 

 front edge, arranged in curved lines parallel with that edge. Above 

 the}' are more sparsely set and, as so often seen in the genus, 

 are arranged in oblique lines passing downward from the front 

 edge, then running transversely and again curving downward. 

 In all probability this is specifically identical with the specimen 

 before alluded to, from the St. Louis limestone, figured by St. 

 John and Worthen and regarded as the same with Leidy's 

 0. vetustus. That specimen was obtained from the St. Louis 

 limestone, at St. Louis, and is now in the museum of Washing- 

 ton University. Mr. Gurlej^'s splendid spine is from the Kinder- 

 hook group. It is quite symmetrical, was unquestionably set on 

 the middle line of the back and has not been much compressed. 



The exposed portion is seven inches in vertical height and 

 was once perhaps half an inch higher. The base is ten inches 

 long, measured from front to rear, and beneath the ornamented 

 portion shows a smooth and slightly incurved band which is so 

 frequently seen in spines of Oracanthus which show the base. 

 The shortness of this buried portion has been a puzzle, since it 

 seemed to prove that the spines were set in the integument of 

 the surface to a very shallow depth and therefore could ha\e had 

 little firmness. But the specimen now before us shows that, on 

 the contrary, by the anterior projection of the base, the spine was 

 prepared to endure a greater strain coming from the front than 

 any other of which we have knowledge. 



Considering the difl^erence of form and ornamentation between 

 this spine and Leidy's type I should have promptl}' decided that 

 the}^ represent different species, but Mr. Gurley sends me another 

 specimen from the Kinderhook group which is certainly not dis- 

 tinct from the large one we have been considering and yet is as 

 much compressed as the type of Dr. Leidy's species. The orna- 

 mentation is much more crowded than in the t3'pe specimen, and, 

 like that on the spine alread}' described, has a far more distinct 

 arrangement in vertical lines, but the ornamentation in this 

 genus is peculiarl}^ variable, as may be seen in the specimens 

 described by Agassiz and Davis. Possibly the accumulation of 

 more material will show that these spines from the Kinderhook 

 group are specifically different from that described by Dr. Leidy, 

 but in the absence of any positive diagnostic features I have hesi- 

 tated to separate them. 



OrACANTITUS PUGIUNCULL'S, St. J. &. W. 



PI. XXII.,fig. 4. 



Ctencanthuspugiuriculus,8t. J. & W., PaliT?ontology of Illinois' 

 Yol. YL, p. 430, pi. 21, figs. !)-9c. 



