VEKTEBKATES. 247 



posteriorly, and are quite uniformly marked by slightly oblique 

 transverse ridges slightly raised and culminating above in a low 

 crest, the unworn slopes and depressions being beautifully sculp- 

 tured logitudinally by delicate thread-like lines crossed by extremely 

 fine transverse or oblique rugae, the lateral edges similarly orna- 

 mented as noticed in the dorsal ridge; the nodose character of the 

 transverse ridges increases toward the postero-lateral angles, how- 

 ever, retaining the details described, and in worn specimens the 

 lateral costae show more or less smooth crests, the extremities of 

 the tubercles producing the pectinated or crenulated lateral borders 

 observed in abraded specimens, like the original or type exam- 

 ple of the species ; the costse increase by bifurcation and implan- 

 tation below at frequent intervals. The intercostal sulci are perhaps 

 one-half the diameter of the ribs, presenting a furrow of moderate 

 depth, striato-punctate, that on either side of the dorsal ridge and 

 others showing occasional irregularly dispersed tubercles orna- 

 mented precisely after the style observed in the costal tubercula- 

 tions. Postero-lateral angles sharply defined, skirted by a narrow, 

 faintly depressed outer belt of the posterior face, which rises into a 

 low angular ridge defining the regularly transversely concave, mod- 

 erately deep median furrow occupying more than half the lateral 

 area, and which is coarsely pitted or striato-punctate; immediately 

 along the outer side of the lateral crests occur a row of depressed, 

 obovate, closely arranged tubercles, spaced by less than half their 

 longer or longitudinal diameter, constricted basally and culmin- 

 ating in a low crest overhanging the upper border, similarly marked 

 by delicate thread-like lines already remarked. The pulp cavity is 

 of moderate capacity, compressed-oval in transverse section, and in 

 an example of at least 150 millimetres in length it extends to 

 within 20 mm. of the distal extremity, apparently opening out in 

 the posterior face little if any above the dorsal line, which latter 

 has a rather oblique upward course from the anterior dorsal angle, 

 inserted base longitudinally striato-punctate, proportionately of con- 

 siderable depth, perhaps equal to a fourth of the entire length of 

 the spine. 



The above description is founded upon two specimens : one, the 

 original examined by Messrs. Newberry and Worthen, representing 

 a small-size spine about 60 millimetres in length, showing one side 

 with patches of the worn costas and dorsal ridge which apparently 

 terminate at the oblique dorsal line; the posterior face is broken 

 away. The other specimen preserves nearly 111 millimetres of a 



