40 
General Form. — Thoug-h a lisli ol‘ the form of that now niuler discus- 
sioii is naturally much distorted, in most cases, when buried in sediment, the 
study of a large scries of specimens seems to reveal approximately its normal 
proportions. The original of PI. YII, Pig. ] , may perhaps be taken as a 
typical example to exhibit the form of the trunk, while the original of PI. 
A'll, Pig. 5, determines the proportions of the caudal pedicle and lin. The 
head occupies a little more than one-tifth of the total length of the body 
(exclusive of the caudal lin), and its height at the anterior margin of the 
operculum is contained slightly more than two-and-a-half times in the 
niaximnm de})th of the trunk. The dorsal tin arises at the commencement 
of the posterior third of the trunk ; and the dorsal margin in advance of this 
is so much arched that, about half-way hctwcon the lin and tlic head, the 
maximum depth of the trunk equals its extreme length from the hack of the 
clavicle to the base of the caudal lin. The pectoral tins are very large, and 
the pelvic fins are placed about half-way between the head and the anal fin, 
while the ventral margin immediately in advance of the latter ]:>erceptiljly 
bulges downwards. The caudal fin is relatively large and powerful. 
Head and Opercular Apparatus.— opercular bones and tlie 
external elements of the head, PI. VII, Pig. 3, exhibit a granular ornamen- 
tation, but little can be discovered of details. The orbit is well marked, 
being surrounded by superficial membrane bones, forming apparently a 
narrow circumorbital ring, bordered postcro-inferiorly by large suborbitals 
{so.) between which tiie sutures are usually indistinct. The membrane-bones 
of the cranial roof arc continued backwards by a large plate extending 
prominently above the operculum ; and between it and the latter element 
there is sometimes a space that may have been occupied by a chain of bones, 
such as has been supposed to occur in C. Fxtonl.^ The operculum {op.) is 
only half as large as the suboj^erculum (.9. op.), and almost triangular in 
shape, owing to the absence of the postero-superior angle ; the sub-operculum 
equals the operculum in width, but is twice as deep ; and beneath the last- 
named bone there are three or four stout ])ranchiostegal rays {br.) sometimes 
distinctly observable. The prcopcrculum was presumahly absent, there being 
scarcely space for it in its ordinary situation ; and no traces of an interoper- 
culum can be recognized. 
Appendicular Skeleton. — Several specimens exhibit ])ortions of a long 
slender clavicle (PI. VII, Pig. 3, d) and a supraclavicle ; but none of the 
* Smith WoodwiU'd, loc. cit, p. Ill, I’l. vi, ilg. 7. 
