186 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
and disappearing, so far as known, with Helicoprion in the Permian of Russia, 
Iudia, and Japan. Occasionally the median azygous series of the lower jaw in 
Cestracion philippr is slightly enlarged, possibly through atavism. The ancient 
family of Cestraciontidae to which all these forms belong is remarkable not 
only for its astonishing longevity, almost unparalleled amongst fishes, but also 
for its prolific offshoots during Palaeozoic and Mesozoic times. The great 
groups of Cochliodonts, Orodonts, Acrodonts, and Hybodonts may all be con- 
sidered as derivatives from the Cestraciont stem, and it is probable that the 
modern ray-type is also descended from the same lineage. 
The great variety in form manifested by the lateral teeth of C. variabilis, 
as implied by the specific title, has been well illustrated by St. John and 
Worthen. Some of the posterior series bear a strong resemblance to those of 
Orodus, but are distinguished by the buttressed condition of the coronal border 
and the less acuminate character of the series of lateral teeth. Only Jaekel 
has expressed an opinion that Orodus and Campodus are not generically dis-_ 
tinct, and are intimately related to Psephodonts and Psammodonts.!_ Examples 
of detached teeth of C. variabilis are shown in Plate 2, Figs. 13 and 14, the 
latter agreeing very closely with St. John and Worthen’s Plate VIIL., Fig. 4, of 
the sixth volume of the Illinois Palaeontology. 
Formation and Locality. — Missourian ; Kansas, Nebraska, Iowa, and Illi- 
nois. 
Ctenacanthus amblyxiphias Cope. 
(Plate 2, Figs. 22, 23.) 
1891. Ctenacanthus amblyxiphias E. D. Cope, Proc. U. S. Nat. Museum, Vol. XIV., 
p. 449, Pl. XX VIIL., Fig. 3. 
This species was originally described from the Permian of Texas, and does 
not appear to have been recognized up to the present time outside of the typi- 
cal locality. The two fragmentary spines obtained by Professor Barbour are 
from the Missourian of South Bend and Louisville, respectively, in Nebraska. 
This form has a more angular cross-section than most of the Mississippian 
species of Ctenacanthus. 
DIPNOI. 
CTENODONTIDAE. 
Sagenodus copeanus WILLIsTon, 
1899. Sagenodus copeanus S. W. Williston, Kansas Univ. Quart., Vol. VIII., p. 178, 
Pl. XXXV.-XXXVII. 
This species is known by the upper dentition and a number of associated 
bones from the Missourian of Brown County, Kansas. 
1 Zeitschr. deutsch. geol. Ges., Vol. LI., 1899, p. 296. 
