VEETEBEATES. 421 



line of insertion and the abrupt posterior deflection in the curvature of 

 the costa?, producing a frayed appearance in that portion of the poste- 

 rior margin, bear close resemblauce to the form which we have indicated 

 under the name G. speciosus, from the same formation ; the peculiar 

 tuberculation of the costne and more robust proportions, however, serve 

 to distinguish it from the last named form, while these and the above 

 mentioned characters offer marked contrast to other forms from the 

 American Carboniferous deposits. In general outline it closely resem- 

 bles G. brevis, Ag., a form originally described by Professor Ag-assiz, 

 from the British Carboniferous limestone. Its differences, however, are 

 obvious at a glance — the costte in G. brevis being far less numerous and 

 not bifurcated, while the tubercles are distinctly marked with radiating 

 carina?. 



Position and locality : In the uppermost beds of the Kinderhook for- 

 mation ; vicinity of Legrande, Marshall county, Iowa. 



Ctenacanthtjs sctjlptus, St. J. and W. 

 pi. xiv, rig. 1. 



Fin-ray of medium size, anterior and posterior margins converging 

 towards the apical extremity at the rate of one-fourth inch in three 

 inches, slightly curved, line of insertion somewhat irregular and form- 

 ing an angle of 35° to 40° with the posterior inclination of the spine. 

 Lateral surfaces flattened and gradually converging to the rounded 

 anterior margin, occupied by numerous, irregularly disposed, rarely 

 bifurcated costae, which more or less regularly diminish in size poste- 

 riorly ; intercostal spaces equally irregular, varying from half to the 

 full -diameter of the ridges, and longitudinally traversed by one to three 

 delicate thread-like carina?. The costte are elegantly ornamented with 

 stellate-sculptured tubercles of variable shape and size in different 

 parts, generally spaced by once or twice their diameter, but sometimes 

 closely approximated ; in the anterior portion of the spine, especially 

 above, they generally occur as oblique or transverse protuberances, 

 abruptly truncated above and sloping inferiorly, and along the anterior 

 margin a slightly eccentric row of relatively large transverse tubercles 

 occur, the bifurcations of which carry longitudinally elongated tubercles, 

 similar to those occurring throughout the lower portion and in the pos- 

 terior costee. Posterior face rather deeply channeled either side of the 

 prominent median ridge, lateral angles prominent, subacute, with indi- 

 cations of a row of small tubercles along the crest in the upper portion 

 of the spine. Base apparently of moderate length, rounded at the 

 extremity, and beautifully striated externally, the thread-like lines ter- 

 minating above in the cost*, the intermediate ones continuous with 



