264 
SELACHII. 
P. 2166 C. Small spine, the exscrted portion measuring 0‘24, and 
the base 0*105 ; a few largo denticles are closely arranged 
^towards the extremity. Egerton Goll. 
P. 2166 g. Imperfect spine, labelled by Agassiz Ifyhodus Jiomojrrion. 
Egerton Coll. 
Hybodus medius, Agassiz. 
1843. Ilyhodua medius, L. Agassiz, Poiss. Foss. vol. iii.p. 184, pi. xxiv. 
fig. 25. 
Type. Group of teeth. 
Teeth with a relatively low crown, the contour gradually rising 
into a median conical pointed eminence ; lateral cones generally 
inconspicuous ; superficial coronal wrinkles numerous and prominent. 
The lateral cones are relatively the hirgost in the most anterior 
teeth ; and the most posterior teeth are not much elongated. 
Form. ^ Loe. Lower Lias : Lyme llcgis, Dorsetshire. 
P. 340. Head and anterior portion of the trunk, preserved upon a 
slab of Lias, 1’17 m. (3 ft. o in.) in length, partly dist urbed 
by the head of an Ichthyosaurus. The specimen is shown 
of one-fifth the natural size, in I’l. VII. fig. 2, and exhibits 
the crushed head and dentition from the lower aspect, 
the partly disturbed axial skeleton of the trunk in side- 
view, and the two dorsal fin-spines ‘. The outlines of 
the pterygo-quadrato (ptq.) and mandibular (md.) carti- 
lages are distinguishable, exhibiting the usual form ; and 
the adjoining extremities of the left hyomandibular (hni.) 
and ccratohyal (ch.) project beyond the loft mandibular 
ramus. The dentition is somewhat scattered, and is closely 
similar to that shown in No. P. 2199, many of the teeth 
having more distinctly separated lateral cones than in 
No. 41103. Obscure traces of the branchial apparatus 
(l>r.) and the pectoral arch (p>ct.) occur behind the head ; 
and still more posteriorly the neural arches and spines 
(na.) arc arranged in broken, though comparatively regu- 
lar series. The latter are broad and elongate, not clearly 
s(!parated at their base, but without any indications of 
intercalary cartilages; and immediately below the series 
is a narrow vacant space, evidently implying the persis- 
tence of the notochord (not.). The abdominiJ region is 
well supported by strong ribs (r.), which are all unfortu- 
nately displaced, crushed, and broken. Towards the 
' The second dorsal spine being detached is not shown in the figure. 
