58 
“ On a Head of Hybodus Delabechei, associated with Dorsal 
Fin-spines, from the Lower Lias of Lyme Begis, Dorsetshire,” 
by A. Smith Woodward, F.GkS., F.Z.S. 
More than forty years ago, Sir Philip Egerton* made known 
the head of a fossil shark from the Wealden of the Isle of 
Wight, exhibiting most of the teeth in natural order in both 
jaws. These teeth displayed much less variation in form and 
characters than those of the predaceous sharks of the present 
day; and, on the evidence of the dentition, the species w r as 
assigned to Ilybodus, under the name of H. basanus. Several 
heads of the same kind have subsequently been discovered in the 
Wealden of Pevensey Bay, Sussex; and considerable information 
has thus been obtained concerning not only the dentition, but 
also the cranial cartilage itself, and the mandibular, hyoid, 
and branchial arches.f 
The teeth of th© Wealden shark, however, are high-crowned, 
compressed, and comparatively smooth, and differ so much from 
the Liassic teeth of Ilybodus that very possibly this late Mesozoic 
species may eventually prove to pertain to a distinct genus. It 
is therefore of great interest to be able to place on record the 
discovery of the head and the greater part of the naturally- 
arranged dentition of a typical species of Hybodus from the Lower 
Lias of Lyme Begis ; and the following notes relate to a fossil 
of this kind preserved in the Peed Collection of the Yorkshire 
Philosophical Society’s Museum. 
The specimen in question is unfortunately compressed, like 
all fossils from the Lias ; but the low r er jaw is conveniently 
displaced to exhibit the dentition, and the shagreen is sufficiently 
sparse to permit the determination of the boundaries of portions 
of the cartilage. The left side of the head is exposed; and the 
whole is shown, of one-quarter the natural size, in Pl. I., Fig. 1, 
while the mouth and dentition are drawn, of the natural size, in 
PI. I., Fig. 2. Outer views of six of the upper teeth, partially 
restored, are also given in PI. I., Figs. 3—8. 
*Sir Philip Egerton, Quart. Journ. Geol. Soc., vol. i. (1845), pp. 197-199, 
pl. iv. 
f Smith Woodward, “ Catal. Fossil Fishes Brit. Mus.,” pt. i. (1889), pp. 273- 
275, pl. xii, figs. 1-4. 
