28 
(/) Portion of the trunk, exhibiting botli pelvic tins and a frag- 
ment of the pectoral, preserved in counterpart. 
{(j) Portion of the trunk, with a fragment of the left pelvic fm, 
and the bases of the dorsal and anal. 
(A) Fragment of large trunk, with pelvic fm (PI. X, Fig. 4). 
General Form . — As shown by the type- specimen (PI. VIII, Fig. 5), 
the trunk is very long and slender, its length being at least three times as 
great as the total length of the head and opercular bones. As in B. glgas 
there is sometimes an indication of a slight deepening of the trunk at the 
commencement of the dorsal and anal fins, though this, again, may perhaps 
be due to crushing during fossilization. As in B. g/gas, also, the pectoral fins 
appear to have been small and delicate. 
Head and Opercular Bones. — The head is shown from beneath in PI. 
VIII, Fig. 5, and from the lateral aspect in PI. X, Fig. 3. The side of the 
skull is superficially ornamented l)y fine vertically directed ridges or striations, 
like those of B. striolatus and B. glgas ; and the mandible is also marked by 
similar striations, curved ujuvards behind, but mainly extending in the 
direction of its long axis. Nothing noteworthy can be observed in the 
characters of the skull or opercular apparatus ; but in the type-specimen the 
mandible is fractured in such a manner as to suggest the presence of an 
elongated anterior azygous element (PI. VIII, Fig 5, ]}S.), similar to that 
already supposed to be a presymphysial bone in the B. acutus of the English 
Lias.* The teeth are imperfectly displayed, and exhibit the usual 
characteristics. 
Axial Skeleton of Trunk. — In every respect the known specimens of 
B. gracilis agree with those of B. glgas already described, in demonstrating 
the persistence of the notochord and the expansion of the bases of the neural 
and hannal arches. These fossils, moreover, correspond in showing that the 
endoskeletal parts wore only superficially calcified or ossified ; and in some 
cases the crushing during fossilization seems to have produced a false appear- 
ance of striation upon the matrix where the obscure remains occur. Strong 
ribs are seen in the type-specimen (PI. VIII, Fig. 5, r), arranged in about 
twenty pairs. 
* Smith Woodward, “ Uu the Mandible of Belonostomun cinclus,” Quart. Jouru. Geol. Soc., 1SS8, Vol. xliv, 
p. 117, ri. vii, fig. 14. 
