96 On the Skeleton of a Chimeroid Fish (Ischyodus). 
end of the comparatively slender exserted portion is laterally 
compressed, though apparently expanding again at the distal 
end, where it is much broken. The denticles originally 
clustered upon this spine are very slender, pointed, sigmoidally 
bent, and fixed upon expanded bases. 
The vertebral column consists, as usual, of a closely 
arranged series of delicate calcified rings, of which five in the 
abdominal region occupy a length of 0°0035 and measure 
0-004 in vertical diameter. 
Of the appendicular skeleton both the pectoral and pelvic 
arches are too imperfectly preserved for description; but the 
elongated claspers are faintly shown, and these do not appear 
to have been provided with dermal hooklets or spines. 
single denticle resting upon the pelvic cartilage may well have 
been displaced from the group on the head. 
The dorsal fin-spine, which measures 0°057 in length, is 
remarkably slender and only slightly arched. The small 
supporting cartilage is conspicuous at its base. In form and 
proportions, and even in the restricted anterior area of the 
superficial striations, it agrees precisely with the small spines 
from the Stonesfield Slate described as Leptacanthus semi- 
striatus *, and, if found at a Lower Oolitic horizon, would 
be thus named without hesitation. In HElasmobranch and 
Chimeeroid fishes, however, the characters of the dorsal fin- 
spines are often unreliable and insuflicient for specific, or even 
generic, determinations. 
No traces of calcified rings in the “ lateral line ” system or 
of dermal tubercles are exhibited ; but the absence at least of 
the former is probably due to their loss in the extrication of 
the fossil from the matrix. 
In conclusion, the Oxfordian fossil now described tends 
further to contirm the reference of the Jschyodus-like fishes to 
the existing family of Chimeride, and a peculiar form of 
“Leptacanthus,” already assumed on theoretical grounds to 
pertain to Ganodus t, is definitely proved to be at least 
Chimeroid. The impossibility of observing the oral surface 
of the dental plates prevents, as already remarked, any satis- 
factory determination; but the external aspect of the den- 
tition so closely resembles that of the well-known Upper- 
Jurassic species Ischyodus Egertoni+ that, until further 
evidence is discovered, the Christian Malford fossil may be 
provisionally quoted as an immature example of that form. 
L. Agassiz, Rech. Poiss. Foss. vol. iii. (1837), p. 28, pl. vii. figs. 3-8. 
Voodward and Sherborn, Cat. Brit. Foss. Vertebrata (1890), p. 114. 
* 
Gian 
{ L, Agassiz, tom, cit. p. 340, pl. xl. e. figs. 1-10. 
