78 bulletin: museum of compakative zoology. 



spines constituted by C. formosus, C. sculptus, C. depressus, O. venustus, 

 C. vetustus, 0. denticulatus and numerous others, which unquestionably 

 belonged to tlie tirst dorsal fin.^ Bearing this generalization in mind, 

 we may pass on to a discussion of some new or little known species of 

 this "genus," chiefly from the Kinderhook division of the Subcarbon- 

 iferous. For the opportunity to describe the types belonging to the 

 United States National Museum at Washington, the writer is greatly 

 indebted to Mr. Frederic A. Lucas, Curator in charge of the Department 

 of Comparative Anatomy. 



SPECIES FOUNDED ON SPINES BELONGING TO THE ANTERIOR 



DORSAL FIN. 



Ctenacanthus longinodosus, sp. nov. 



Plate 5, Fig. 2. 



As type of this species is selected a unique specimen belonging to the 

 United States National Museum (Cat. No. 3393), and derived from the 

 Kinderhook Limestone of the Mississippi Valley, probably from near 

 Burlington, Iowa. It was formerly in the private collection of Mr. L.» 

 A. Cox, of Keokuk, Iowa. The spine is unfortunately not preserved in 

 its entirety, the distal third or fourth and nearly all of the inserted 

 portion having been broken away. It has also been subjected to some 

 deformation, especially in the distal portion, prior to or during fos- 

 silization, and the walls of the pulp cavity have been forced inward 

 by pressure. 



Notwithstanding these imperfections, the spine is of much interest, 

 and its unique style of ornamentation serves to distinguish it at once 

 from all other species. About sixteen broad, flattened and highly 

 polished costfe have their origin along the base of insertion, and are 

 continuous throughout the length of the spine. They are parallel and 

 non-bifurcating, and only a few small and incomplete adventitious ridges 

 are intercalated between them, or engrafted upon their sides. The 

 principal costae are not all of uniform width or thickness, nor are they 

 separated by regular intervals, some being narrower and more closely 

 spaced than others. The intercostal spaces are plane and covered with 

 fine longitudinal rugge of precisely the same appearance as those of the 

 inserted portion. The costae are remarkable for their development at 



1 Science, n. s., Vol. XIV. (1901), p. 795. 



