256 PALEONTOLOGY OF ILLINOIS. 



the lateral surface of this side the tubercles consist of simple, irreg- 

 ularly-conical, radiately- sculptured prominences, their apices directed 

 upward, sometimes coalescing in the oblique rows, forming irregular, 

 sharp crests spanning two or more of the obscure costae. Similarly 

 confluent, larger tubercles are met with in either border, where they 

 form asymmetrically-oblique rows, with indications of a curving up- 

 ward on gaining the left side, but presenting individual variation in 

 the latter respect no two specimens actually agreeing. 



In regard to the correspondence of the characters of opposite 

 flanks of these spines, the fine example described by Dr. Leidy offers 

 most conclusive evidence bearing on their dissimilarity, and which 

 might readily confuse identifications based on unique specimens, 

 showing opposite sides of the spine. The latter shows an individual 

 of about the same dimensions as the example above alluded to, free 

 from the matrix of " iron-gray limestone," revealing both sides of 

 the spine, the anterior border of which, unfortunately, has been 

 worn smooth obliterating the tuberculation. Compared with the St. 

 Louis specimen, the right-side tuberculation shows approximately 

 the same disposition in oblique rows ascending from either border 

 and meeting in the middle where their continuity is interrupted. 

 In the left side "the tubercles are arranged more regularly in lon- 

 gitudinal rows, and they evince a tendency to become confluent in 

 short transverse rows, which pursue an irregular waving course 

 across the ray," with a general slight obliquity ascending from near 

 the anterior border where the large confluent tubercles are rather 

 suddenly deflected upward and cross the edge obliquely, diminishing 

 as they approach the right flank, precisely as shown in the fragment 

 originally described by the authors (0. consimilis, vol. VI, PI. XXII, 

 f. loc). The posterior border is occupied by three or more longi- 

 tudinal rows of tubercles, laterally compressed, the margin in the 

 left side being occupied by a row of confluent tubercles obliquely 

 curved upward exactly in the opposite direction to the similar row 

 in the same side at the anterior border. The example noticed by 

 Dr. Leidy is reported as having been derived from the Carboniferous 

 limestone of Missouri Territory; the exact formation and locality, 

 however, are unknown. 



It may well be questioned whether these spines occupied a dorsal 

 rather than a lateral position on the body of the fish. Their flanks, 

 instead of presenting that absolute symmetry characteristic of dorsal 

 rays, at least so far as relates to the tuberculose ornamentation, 

 show marked asymmetrical features which may be more in accord 



