VERTEBRATES. 255 



GENUS ORACANTHUS, Agassiz. 

 OBACANTHUS VETUSTUS, Leidy. 



PI. XXIV, Fig. 2. 



Oracanthus vetustus, LEIDY, 1856. Jour. Acad. Nat. Sci., Phila., 2d series, ill. p. 161, PI. 16, 



f. 1, 2, a. 

 Oracanthus consimilis, St.;J. and W., 1875. III. Geol, Surv. VI, p. 476. PI. XXII, f. 15. 



The cabinet of Washington University, of St. Louis, contains a 

 fine large spine, which, we have no doubt, is specifically identical with 

 the form originally described by Dr. Leidy under the above desig- 

 nation, and which was subsequently noticed by the authors under the 

 name Oracanthus consimilis. This specimen, however, affords a much 

 more satisfactory idea of the superficial characteristics of the spine 

 than it was possible to gain from the fragmentary material acces- 

 sible to us at the time the latter notice was prepared, and we are 

 thankful for the opportunity of correcting and extending the notice 

 of the species, which we owe to Dr. Hambach, of that institution, 

 and to Dr. Leidy, who kindly secured the loan of the type specimen 

 from the museum of the Academy of Natural Science. 



The above mentioned specimen preserves a length of 15 centimetres, 

 and a width of above 6 c. m., the basal margin and a portion of the 

 left side being broken away, exposing the large pulp cavity. The 

 outline is that of a moderately backward-curved, rapidly-tapering, 

 laterally-compressed cone, terminating in a sharp point ; the anterior 

 edge broadly and regularly rounded into the gently-convex lateral 

 surfaces ; the concave posterior border somewhat flattened and more 

 snarply rounded, but without defined postero-lateral angles. The 

 walls of the pulp cavity are moderately thick, presenting the great- 

 est thickness along the convex anterior border, the lateral walls more 

 or less crushed in by pressure. The exposed surfaces of the spine 

 show obscure, irregular longitudinal costae, and are thickly studded 

 with tubercles, which assume a variety of shapes, according to their 

 position, and ranged in distinct, though interrupted obliquely trans- 

 verse rows, which, in the right side, rise from the anterior edge up- 

 ward and backward to a point near the middle, where they meet 

 similar rows rising obliquely from the concave border in the opposite 

 direction ; but toward the base, where the tubercles are more crowded 

 and larger, this oblique course is less conspicuous, while their longi- 

 tudinal disposition is more or less distinctly marked throughout. Over 



