60 
by all the portions of the teeth of each series sufficiently 
preserved, the partial restorations given in Figs. 3—8 seem 
justifiable, and illustrate the main features. These teeth 
pertain, as indicated, to series v.—x.; and it will be observed 
that, compared with those of the lower jaw, they are more 
elongated and exhibit less elevated crowns. 
The shagreen, scattered over the whole of the fossil, is of the 
usual type already often met with in the Liassic species of 
Hybodus and Acrodus, i.e.,conical granules, radiatel) sculptured. 
In size, however, these granules are remarkably small; and 
especially noteworthy is the absence of the well-known hook¬ 
shaped head-spines ( Sphenonchus ). 
As shown by the dentition, the fossil just described pertains 
to Hybodus Delabechei, Charlesworth,* of which numerous groups 
of teeth are already known, besides a shagreen-covered head.f 
This species, indeed, was the first to reveal the true nature of 
the so-called Sphenonchus; and it now gives the first information 
as to the number and proportions of the dental series in the jaw 
of the typical members of the genus to which it belongs. 
Neither of the two Liassic species of Acrodus exhibits more 
than eight or nine series of teeth in each ramus of the jaw 7 ^ ; 
and Hybodus medius , which closely approaches Acrodus , also 
appears to possess only eight* 
The dorsal fin-spines found in association with the head are of 
the same kind as those already proved to pertain in part to 
H. Delabechei by specimens in the British Museum. The exserted 
portion of the anterior spine measured about 14 inches* in 
length when complete, and If inches in maximum breadth 
across the base ; while the corresponding measurements of the 
posterior spine are ll£ inches and If inches. Each spine is thus 
robust, and the lateral ribs are numerous and closely arranged ; 
the posterior denticles are very large, and placed in the case of 
the anterior spine, upon a median longitudinal elevation. 
*E. Charlesworth, Mag. Nat. Hist., N.S., vol. iii, pp. 242 — 246, pi. iv. See 
also“Catal. Foss. Fishes Brit. Mas.,” pt. i, pp. 259—262, pi. viii, pi. x, figs. 1—5. 
fE. C. H. Day, Geol. Mag., vol. ii (1865), p. 565. Figure given in “ Catal. 
Foss. Fishes Brit. Mus.,” pt. i, pi. viii. 
JE. C. H. Day, Geol. Mag., vol. i (1864), pp. 57—65, pi. iv. “Catal. Foss. 
Fishes Brit. Mus.,” pt. i, pp. 283—293, pis. xiii, xiv. 
*“ Catal. Foss. Fishes Brit. Mus.,” pt. i, p. 265, pi. ix. 
^Present measurement 12§ inches. 
