EASTMAN: CARBONIFEROUS SHARKS. 81 
dorsal fin. From other described species it is readily distinguished by 
its peculiar ornamentation. 
The lateral face is ornamented with twenty regularly spaced longitu- 
dinal costs, which continue perfectly straight without bifurcation, and 
are surmounted by conical or rounded tubercles separated by intervals 
equal to their own diameters. Some of the tubercles belonging to the 
anterior costze show a tendency to become obliquely elongated, as in 
C. solidus and C. decussatus, and those of the posterior cost are often 
delicately striated. None of the costz exhibit a tendency toward pos- 
terior deflection, such as commonly occurs amongst other species; and 
the peculiar beaded appearance of the tubercles is quite remarkable for 
this genus. The passage of tubercles into transverse ridges, such as 
we have observed in the newly formed costz of C. long?- 
nodosus, or in the latest formed portions of older costa, 
is not evident in the present species, where the primitive 
tuberculated style of ornament seems to have been per- 
manently retained. No costz appear along the rounded 
anterior margin, which has been worn quite smooth prior 
to fossilization. The spine is preserved for a length of 
12.5 cm., and the inserted portion has a maximum width 
of 3.4 cm. The cross-section shown in text-figure 9 is 
taken across the line of fracture where the rest of the 
spine has been broken away ; the width hereis 3cm.and Ctenacanthus 
the thickness 1.4 cm. lucasi, sp. 
The specific title is bestowed in honor of Mr. Frederic cpt 
A. Lucas, of Washington, to whom the writer is indebted spine. X . 
for many courtesies, and for the loan of much valuable 
material. The original is preserved in the United States National 
Museum (Cat. No. 4844), and was collected by Mr. L. A. Cox from the 
Kinderhook Limestone, presumably in Iowa. 
Formation and Locality. — Kinderhook Limestone ; Iowa (?) 
Fia. 9. 
Ctenacanthus venustus, sp. nov. 
Plate 3, Fig. 2. 
Two examples are known of this species, the larger of which belongs 
to the Worthen Collection in the Museum of Comparative Zodlogy, and 
is selected as the type. The smaller spine, shown in Plate 3, Figure 2, 
belongs to the United States National Museum (Cat. No. 3385), and 
was formerly the property of Mr. L. A. Cox, of Keokuk, Iowa. Both 
