254 PALEONTOLOGY OF ILLINOIS. 



walls, and m which respects intimate relationship with Batacanthus 

 is disclosed. The lateral surfaces display numerous narrow longitu- 

 dinal ridges, spaced by intervening shallow sulci, in width a little 

 more than the diameter of the ridges, and irregularly, coarsely pitted. 

 The costae apparently occupy the entire surface, save a belt extend- 

 ing along either side of the posterior angle, where they are obsolete, 

 or at least less marked. Perhaps the most interesting feature is 

 that observed in connection with the tuberculation : The carina along 

 the anterior edge sends off at irregular, alternate intervals a strong 

 low tubercle, which fills the adjacent sulcus, even crowding over 

 upon or enveloping the next parallel ridge ; similar, somewhat 

 smaller tumid tubercles are dispersed with greater or less irregular- 

 ity over the body of the spine, where, in the worn condition of the 

 specimen, they often have the appearance of occupying the sulci, 

 and toward the apex becoming confluent and stretching across two 

 or more costse. The tubercles in the belt along the posterior edge 

 are relatively large, irregularly subconical, and ranged in two or 

 three irregular rows ; they are mostly worn quite smooth, but there 

 are vestiges of radiate ornamentation still visible. 



Compared with previously described spines, the present form, per- 

 haps, finds its nearest ally in the Batacanthus stellatus, of the Keo- 

 kuk limestone. It is distinguished, however, from that species by its 

 more compressed lenticular transverse section and the distinct an- 

 gulation of the anterior and posterior edges ; also, the distinct char- 

 acter and disposition of the tuberculation; the anterior edge, also, 

 does not preserve the large, claw-like tenticles that appear in the 

 above species, but these may have been broken off, and even their 

 bases obliterated by abrasion. The distinct angulation of the anterior, 

 and especially the posterior edge, presents an anomalous character, 

 in contrast with the rounded borders of Batacanthus, as represented 

 by the species B. stellatus (N. and W., sp.,) and B. baculiformis, St. J. 

 and W. ; but the unique example before us is not sufficiently entire 

 to permit comparisons necessary in order to determine its exact 

 generic relationship, while such characters as are discernible bear 

 marked resemblance to those attributed to Batacanthus. 



Geological position and locality: Keokuk limestone, upper beds ; Keo- 

 kuk, Iowa. 



