478 PALEONTOLOGY OF ILLINOIS. 



small subcorneal tubercles, very variable and irregularly disposed as to 

 size, but with indistinct traces of longitudinal ridges, which, however, are 

 subject to frequent interruption by the interpolation of large tubercles, 

 which is especially the case towards the summit, and with obscure, 

 irregular oblique disposition ; the lateral tubercles also present a coarse 

 punctation in their worn crowns, with indications of vertical or radia- 

 ting ridges in their sides. 



The decussated^anterior ridge, or transverse tubercles, resemble the 

 decussated ridges of Gtenacanthus ; but this appearance cannot be asso- 

 ciated with any of the Gtenaoanthi occurring in the same horizon, while 

 the character of the very irregular tuberculose lateral surfaces exhibit 

 still more remote affinities with these forms. The unique example, 

 however, is scarcely sufficient for the determination of its generic rela- 

 tionship. 



Position and locality : Fish-bed horizon upper part of the Keokuk 

 limestone ; Warsaw, Illinois. 



ORA04NTHUS consemilis, St. J. and W. 



PI. XXII, Fig. 15. 



The form here indicated is represented by a few fragmentary speci- 

 mens, which generally show only the surface tuberculation, with the 

 exception of a single individual discovered by Mr. Van Horne, which 

 exhibits the entire transverse outline of a section apparently from near 

 the middle of a medium-sized spine. The latter specimen, which is 

 much distorted by the compression of the lateral walls of the large pulp- 

 cavity, indicates a moderately or somewhat rapidly tapering outline, 

 long elliptic transverse section, laterally very gently arched, and the 

 anterior border, as indicated by the apparent greater thickness of the 

 wall in that portion of the spine, is broadly rounded and apparently 

 very slightly curved backward or nearly straight; the opposite or post- 

 erior side faintly concave vertically, relatively broader and more angu- 

 larly rounded, or flattened along the median region and somewhat 

 abruptly rounding into the lateral faces along the posterolateral angles. 

 The superficial ornamentation consists of relatively large, transverse 

 or oval, vertically sculptured tubercles, arranged upon obscure longitu- 

 dinal ridges separated by faint sulci and striato-puuetate, closely 

 approximated laterally, vertically spaced by about twice their diameter, 

 disposed in irregular transverse oi'der, or generally descending in a 

 slight oblique course from the anterior to the posterior border, and uni- 

 formly dispersed throughout the spine, occurring equally in the post- 

 erior and anterior margins. The tubercles culminate in a subacute apex 

 directed towards the summit of the spine, the inferior slope gently con- 



