EASTMAN: CARBONIFEROUS SHARKS. 
91 
figure 13) than C. spectabilis, and the sharp marginal ridge of that 
species is here replaced by a row of tubercles somewhat coarser or more 
elongated than the rest. This latter condition approximates that ob- 
served in C. coxianus from the Keokuk limestone. 
In C. mayt about a dozen longitudinal costz are to be counted along 
the line of insertion ; in C. coxianus as many as 18 or 20; in C. solidus 
upwards of 30; in C. spectabilis about 50; and in C. varians 80 or 
more. Amongst these only C. varians agrees with the species under 
discussion in having sculptured or striated tubercles, and 
this character is also common to C. brevis from the Lower 
Carboniferous of Ireland, and to C. longinodosus, as de- 
scribed above. It is thus apparent that the number and 
direction of the costs are of prime importance in the 
distinction of species. 
The spine shown in Plate 7, Figure 3, is preserved for 
a length of 9.5 cm. and has a maximum width of 3.5 cm. 
The type-specimen belonging to the United States Na- 
tional Museum has the coste more perfectly preserved than 
either of the co-types. Its cross-section, shown in the 
accompanying text-figure 13, is well displayed by the frac- 
ture across the base, but the thickness at this point is 
exceeded by both of the co-types. None of these spines 
retain traces of posterior denticles, although it is very 
probable that such were formerly present. 
Formation and Locality. — Kinderhook; Iowa and 
Illinois. 
Fig. 13. 
Ctenacanthus 
solidus, sp. 
nov. Cross- 
section of 
ty pe - speci- 
men in its 
basal por; 
tion. X +. 
LIST OF SPECIES OF CTENACANTHUS OCCURRING IN THE 
MISSISSIPPIAN SERIES. 
NAME OF SPECIEs. 
Sia 
o j=) 
ao] 
5 a 
Goes 
— = 
se! Q 
. C. coxianus St. J. and W. 
. C. decussatus Eastm. . 
. C. depressus Newb. 
. C. longinodosus Kastm. 
. C. lucasi Eastm. 
KK KK OK 
St. Louis. 
