CESIEACIONIID^. 
259 
placed more or loss mesially, with two or three smaller 
cusps on either side ; the superficial coronal wrinkles are 
few and largo, and the base of the tooth in each case is 
somewhat depressed. Portions of the branchial apparatus 
are preserved, but the number and proportions of the 
arches cannot bo determined. Still more posteriorly aro 
to be observed the two long slender halves of the pectoral 
arch, tai>ering above; each division measures about O'l in 
length, but it cannot be determined whether they were 
united ventrally. The dorsal fin-spine is not much broken ; 
the base is about equal in size to the oxserted part ; the 
posterior denticles are very largo ; and the lateral orna- 
mental ribs are few, widely spaced, and sharp. In those 
characters the spine much resembles that named by Agassiz 
][. croissispinua. Ennislcillen Coll. 
11262, 11282. Two groups of small low-crowned teeth, with the 
cusps slightly oblique, bearing the MS. name of Ilijbodus 
homopryon, Agassiz. Mantell Coll, 
Hybodus delabechei, Charlesworth. 
1839. Hybodus delabechei, E. Charlesworth, Mag. Nat. Hist. n. s. 
vol. iii. p. 242, pi. iv. 
184;l. Hybodus pyramidalis, L. Agassiz, Poiss. Foss. vol. iii. p. 182, 
pi. xxii. a. figs. 20, 21 . 
186.5. Hybodus delabechei, E. C. 11. Day, C eol. Mag. vol. ii. p. 565. 
Type. Imperfect head associated with dorsal fin-spines. 
Teeth with a relatively low crown, the median eminence largo 
and prominent, conical or pyramidal, with two, three, or four small 
lateral cones of similar form ; superficial coronal wrinkles numerous, 
acute. The median coronal eminence is relatively the largest and 
broadest in the principal lateral teeth ; and both it and the lateral 
cones aro narrowest and highest in the symphysial teeth. The 
hindermost lateral teeth are small, very low, long, and narrow, and 
have the cones rounder than in other parts of the dentition. 
The type specimen of U. pyramidalis appears to have been de- 
scribed only from the drawing, which is misleading, inasmuch as it 
does not exhibit the considerable variations of the teeth in the 
associated group. 
Form. ^ Loc. Lower Lias : Lyme llegis, Dorsetshire. 
39880. Crushed head and anterior portion of the trunk, exhibiting 
the shagreen, cephalic spines, and a few teeth, shown, of 
