442 PALEONTOLOGY OF ILLINOIS. 



inbeveled keel ; lateral surfaces moderately arched transversely, occu- 

 pied by five or more longitudinal rows of rather strong, closely approxi- 

 mated tubercles, which are arranged in such order as to form diagonal 

 rows in either direction, those along the posterolateral angles being 

 slightly smaller and apparently more conical. Posterior face abruptly 

 truncated and longitudinally channeled by a rather deep, angular 

 depression. Pulp cavity confined to the posterior half of the spine in 

 the middle, compressed, oval in transverse section. Base deeply 

 imbedded, pointed, dorsal line indicating posterior inclination of spine 

 equal to 20°. 



The characters above noticed are clearly shown, notwithstanding the 

 imperfect condition of the unique example. The surface ornamenta- 

 tion has been obliterated with the exception of a small area, in which the 

 bases of the tubercles are distinctly shown, besides a few apparently 

 worn tubercles, which present faiut traces of vertical or radiating sulci. 

 The tubercles forming the row adjacent to the postero-lateral angles 

 are slightly compressed laterally, but not hooked. A section obtained 

 by breaking the specimen across the middle indicates a rather deep, 

 angular depression in the posterior face, with slightly convex sides 

 rounding into posterolateral angles. Whether the channeled condition 

 of the posterior face is due to the imperfect or mutilated state of the 

 specimen, we have not been able to determine ; but the strongl.v keeled 

 condition of the St. Louis species, G. stellatus, would seem to indicate 

 that such is probably the case, and that the thin posterior walls have 

 been forced in upon the pulp cavity by pressure. 



Position and locality : Lower division of the Chester limestone ; 

 Fountain Bluff, Jackson county, Illinois. 



GfESUB ANACLITACAXTHUS, St. J. and W. 



A fragment of a large dorsal spine, obtained by Mr. Wachsmxjth 

 from the Upper Burlington fish-bed, presents anomalous characters 

 which seem to indicate generic relationship with none of the several 

 ichthyodornlites with which it is associated. Unfortunately the speci- 

 men is imperfect, bearing evidence of distortion from pressure by which 

 parts of the spine are so thrown out of place as to render the determi- 

 nation of the section and entire outline exceedingly difficult, if not 

 wholly unsatisfactory. Apparently, so far as it is possible to ascertain, 

 both sides present quite the same appearance, from which fact it is 

 inferred that the fragment before us may be relied upon for such char- 

 acteristic features as have not been destroyed by mechanical attrition 

 and pressure. Towards the lower extremity the spine has been frac- 

 tured across, and the anterior edge so folded under and broken as to 



