422 PALAEONTOLOGY OF ILLINOIS. 



those occupying the intercostal furrows ; posterior face deeply excavated 

 by the pulp cavity, which latter occupies above half the transverse dia- 

 meter of the spine a third the distance from the apex, sublenticular in 

 section. 



The above description is based upon a beautiful specimen discovered 

 by Mr. WAchshtjth, which presents a nearly entire and well-preserved 

 spine, above six inches in length. In general outline, and number of 

 costse, it strikiugly resembles G. fortnosus, Newb., a form occurring in a 

 similar horizon, the Waverly formation of Ohio. But the costse in the 

 present form bear distinctly sculptured tubercles, which do not appear 

 as simple decussations, being quite isolated or separated by spaces des- 

 titute of enamel, and extremely diverse in shape ; also, the posterior 

 face instead of being "flattened and slightly concave," is distinctly cari- 

 nated longitudinally. As represented in the unique specimen described, 

 it constitutes a remarkably -well-defined and readily distinguishable 

 form. 



Position and locality : In the lower fish-bed (No. 1) of the Upper 

 Kinderhook beds ; Burlington, Iowa. 



Ctenacanthus varians, St. J. and "W. 



PI. XIV, Kg. 2. 



Fin-spine of robust proportions, rapidly tapering from the broadly 

 expanded basal line, elliptical in transverse section. Anterior margin 

 rounded, nearly straight below, but gently arched above, lateral faces 

 flattened posteriorly and gently rounded in front, and occupied by 

 numerous longitudinal ridges, which more or less regularly diminish in 

 size towards the posterior borders, where they are less than one-fourth 

 the bulk of the anterior costse, that along the anterior margin being 

 perceptibly stronger and frequently bifurcated descending towards the 

 basal line; intercostal spaces forming narrow and usually angular 

 channels traversed by a line of minute punctse, in front very crowded, 

 but more irregular in width behind, where they sometimes equal the 

 diameter of the costse. The costse are ornamented by beautifully 

 sculptured tubercles of diverse shape and variously disposed in different 

 parts of the spine ; in the front ridges they frequently form double, 

 rarely triple, rows, which are separated by a faint depression, but still 

 very irregular, the pairs of nearly circular tubercles often coalesce 

 forming a single transverse tubercle, which latter is the prevailing, if 

 not persistent, form in the posterior costse ; in appearance they gener- 

 ally present a broad, gently convex, sometimes concave, inferior slope, 

 sculptured by delicate ridges converging toward the apex, with a more 

 or less well-defined transverse crest and abrupt descent above, spaced 



