78 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
spines constituted by C. formosus, C. sculptus, C. depressus, C. venustus, 
C. vetustus, C. denticulatus and numerous others, which unquestionably 
belonged to the first 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. 
v 
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 coste 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 cost 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 rug of precisely the same appearance as those of the 
inserted portion. The coste# are remarkable for their development at 
1 Science, n. s., Vol. XIV. (1901), p. 795. 
