. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 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 G. coxianus from the Keokuk limestone. In C. mayi about a dozen longitudinal costse are to be counted along the line of insertion ; in C. coxianus as many as 18 or 20 ; in G. solidus upwards of 30 ; in G, spectabilis about 50 ; and in G. varians 80 or more. A
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 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 G. coxianus from the Keokuk limestone. In C. mayi about a dozen longitudinal costse are to be counted along the line of insertion ; in C. coxianus as many as 18 or 20 ; in G. solidus upwards of 30 ; in G, spectabilis about 50 ; and in G. varians 80 or more. Amongst these only G. varians agrees with the species under discussion in having sculptured or striated tubercles, and this character is also common to G. brevis from the Lower Carboniferous of Ireland, and to G. longinodosus, as de- scribed above. It is thus apparent that the number and direction of the costse are of prime importance in the distinction of species. The spine shown in Plate 7, Figure 3, is preserved for a length of cm. and has a maximum width of cm. The type-specimen belonging to the United States Na- tional Museum has the costse 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 Fig. 13. Ctenacanthus solidus, sp. nov. Cross- section of type - speci- men in its basal por^, tion. X {. LIST OF SPECIES OF CTENACANTHUS OCCURRING IN THE MISSISSIPPIAN SERIES. Name of Species. o o .£5 u ® a M a o a 3 o 2 '3 o o 1. C. coxianus St. J. and W. . X ___ X 2. C. decussatus Eastm X — — — 3. C. depressus Newb X — — — 4. C. longinodosus Eastm X — — — 5. C. lucasi Eastm X — — —. Please n
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