VERTEBRATES. 371 



flattened, enamelled carinae, separated by sulci which are lon- 

 gitudinally striated. These sulci are very unequal in width, 

 the anterior one being much the broadest, occupying nearly 

 half the lateral surface, and set with enamelled tubercles, 

 forming a single row above, below irregularly scattered. The 

 posterior denticles are not distinctly shown in the only speci- 

 men obtained. 



This species is clearly generically identical with those described by Agassiz 

 and McCoy (British Palseoz. fossils, pp. 615, 616, pi. SK, figs. 22, 23, 24), and 

 forms an interesting addition to the genera common to the Lower Carboniferous 

 strata of the old and new worlds. From the two species to which reference has 

 been made^this is, however, distinguishable. From A. ornatus, Ag., it is sepa- 

 rated by its single longitudinal band of tubercles, and its larger number of 

 lateral carinae. From A. semi ornatus, McCoy, it differs in its triangular sec- 

 tion being much less compressed laterally, and in the greater inequality in the 

 breadth of the sulci. 



Formation and locality : Burlington limestone ; Quincy, Illinois. 



GENUS LISTRACANTHUS, N. and W. 



SPINES small, gently arched, flattened, thin; sides marked 

 by numerous sharp longitudinal carinse, edges set with many 

 divergent slender acute teeth, those on the convex margin 

 most numerous and largest; base abruptly expanded, and 

 obliquely truncated. 



These spines are considerably unlike any hitherto described. They are 

 marked on the sides somewhat "like Leptacanthus, but are flatter, shorter, and 

 more rapidly narrowed above, while the bristling, divergent teeth of both mar- 

 gins serve to distinguish them at a glance. The base is different from that of 

 most defensive spines, as it is abruptly truncated and expanded : showing that 

 it was set on the surface and did not penetrate the integuments. 



In this respect these spines resemble those of Climatius, as well as those of 

 some recent scaled fishes (Gaslerostcous, etc.), and may be considered modified 

 scales or cranial scutes. They were probably attached by their broad bases to 

 the body or head, serving perhaps both for ornament and defense. 



