The Fossil Elasmobranch Fishes. 370 
those of Hybodus and Acrodus. Palg@ospinax (Thyellina), placed 
by Agassiz among the Squalide, now passes to this family; and 
some interesting specimens of the genus are described, including one 
new species from the Lias of Ohmden. A closely allied form is the 
author’s Cretaceous genus Synechodus, originally referred to the 
genus Hybodus, and known by jaws, teeth, fragments of cartilage, 
vertebra and shagreen. 
To the genus Cesétracion, the last of the group, is referred Sir 
Philip Egerton’s genus Drepanephorus. Six new species of as many 
genera are described; and most of the types, either wholly or in 
part, are in this collection. 
The ScyLuiip# come next with seven genera. The first, Palgo- 
scyllium, is represented by one species (P. minus), anew one from the 
_ Kimmeridgian of Bavaria. Scyllium follows with six species, all 
Cretaceous, two being new, S. dubium from the Lower Chalk, 
Dover, and S. (?) tumidens from the Lebanon. Cantioscyllium decipiens 
is a new genus and species, founded upon the character of the denti- 
tion, recently exposed by the removal of the matrix on one of Agassiz’s 
figured types (tom. iii. pl. xxxviii. fig. 2) of Scylliodus antiquus. 
To the Lamnip# are assigned eight genera, represented by forty-six 
species; but the teeth of the fossil genera are separated by 
characters so slight that it is difficult in some instances to distinguish 
them. Thus Qudontaspis only seems to differ from Lamna in ‘the 
greater relative size and more subulate character of its anterior 
teeth.”  Oxyrhina, again, “only differing from Lamna in the pre- 
vailing absence of lateral denticles in the teeth.” Again, Lamna, 
by Oxyrhina mantelli, “appears to be connected with Oxyrhina; 
and by Lamna obliqua, with Carcharodon.” Orthacodus is a new 
generic name proposed for Agassiz’s Lamna (Sphenodus) longidens, and 
Scapanorhynchus is another new genus founded upon several more 
or less perfect specimens from the Lebanon Cretaceous beds, and 
replaces the genus Rhinognathus of J. W. Davis; from the same 
locality a new species (S. elongatus) is described, and a tooth 
(S. gigas) from the Cambridge Greensand. To the same genus are 
also assigned the Cretaceous teeth respectively known as Lamna 
(Odontaspis) rhaphiodon and L, subulata. 
To Odontaspis are assigned the teeth universally known as Lamna 
elegans, also the other species of Lamna having the same general 
form of tooth. Otodus disappears, the species being absorbed in the 
genus Zamna, which is thus defined: “ Dentition only differing from 
that of Odontaspis in the relatively less elevated and less subulate 
character of the anterior teeth, and the usually larger size of the 
lateral denticles.” One new species is described. Then comes Car- 
charodon with five species, all of Tertiary origin. One species, C. 
megalodon, attained an enormous size, and was very widely distributed. 
The teeth referred to the genus Corax are comparatively small, com- 
pressed and serrated. 
The last family isthe CarcHartpm. Of the type genus Carcharias, 
species of three of its five subgenera are in the collection, and there are 
two new species. The other genera composing the family, and repre- 
sented by species, are Galeocerdo, Hemipristis, Galeus (?), and Sphyrna. 
