VEETBBEATES. 425 



sated costse, the narrow, transverse, vertically ridged tubercles restiug 

 in various directions and degrees of obliquity, generally abruptly 

 descending and sometimes inbeveled above, more gently sloping in the 

 lower side, usually sculptured with a few delicate vertical ridges, or 

 often quite smooth, scalloped along the crest or deeply cleft, sometimes 

 widely spaced, again separated by vertical spaces of scarcely more tban 

 their own diameter. Under an ordinary lens they present the most 

 beautiful appearance, the varied details appearing in all parts and always 

 associated with the transverse style of tuberculation. 



The collections contain several fragmentary specimens of the form 

 described, indicating spines of various dimensions, of which the tine 

 example, figured PI. XIV, fig. 3a, was probably above eight inches in 

 length. As above remarked, in general outline these spines resem 

 ble C. spectdbilis and C. varians; from the former, however, it distinctly 

 differs in ornamentation, and its laterally compressed and less robust 

 figure equally distinguishes it from both the above named forms. In 

 the details of ornamentation, as the form and sculpturing of the indi- 

 vidual tubercles, it more closely resembles the latter form ; but the 

 double arrangement of tubercles, as well as the frequent tendency to 

 become longitudinally elongated in the latter, afford ample distinctive 

 features by which the form under consideration may be recognized. 



Position and locality: All authentic examples of the form at present 

 known pertain to the lower icthyic bed of the Kinderhook formation ; 

 Burlington, Iowa. 



Ctenacsnthus gradocosttjs, St. J. and W. 



PI. XV. Fig. 2, 3. 



Fin-ray moderately strong, long, gradually tapering towards the apex, 

 gently curved, lenticular or long-elliptical in transverse section. Lateral 

 faces flattened for half or two-thirds their posterior diameter, thence 

 somewhat rapidly converging to the anterior margin, along which 

 extends a narrow, compressed, or sometimes rounded ridge, usually 

 smooth along the crest, but in some specimens possessing well-marked 

 lateral prominences, and which are really connected forming singular 

 transverse tubercles, the lateral wings of which are more or less cres- 

 cent-shaped, with the convexity directed upward; the costse are promi- 

 nent, more or less decreasing in size posteriorly, and beautifully wrought 

 in apparently plain transverse tubercles throughout, though they are 

 less distinct in the posterior than in the middle and anterior ridges, and 

 separated by a space half to twice their diameter ; the tubercles vary 

 in shape from more or less obtuse prominences to narrow bands clasp- 

 ing the ridge in variable degrees and directions of obliquity, and in all 



—55 . 



