REPORT ON FOSSIL FISHES. oT 
examination is entered into that a detailed comparison is quite unnecessary. 
Indeed, the structure of the pectoral fin seems to forbid its being placed in the 
genus Rhadinichthys at all, for that member, so far as can be seen, has its rays 
articulated as in the species of Elonichthys of the “ Robisont” type, from which 
it is however excluded by the backward position of the dorsal fin. However, 
rather than hastily to proceed to the creation of a new genus upon that 
character alone, I have placed it provisionally in Rhadinichthys, which it 
certainly resembles more than any other in general contour. 
Genus Cycloptychius (Huxley), Young, 1865. 
(Young, British Assoc. Reports, 1865, vol. xxxv. p. 318; Traquair, Geol. Mag. Decade II. 
vol, i, No. 6, June 1874). 
Cycloptychius concentricus, sp. noy., Traquair. 
Pl. IL. figs. 17-20. 
Description.—The largest specimen attains a length of 42 inches, if we allow 
for a small portion of the front of the head which is broken off. The length of 
the head is contained about 5 times, the greatest depth of the body 63 times, 
in the estimated total, up to the extreme end of the upper caudal lobe. The 
contour of the fish is therefore peculiarly slender and graceful, the depth of the 
body continuing pretty uniform as far as the origin of the posteriorly placed 
dorsal fin, whence it tapers to the moderately stout tail pedicle. 
The head is somewhat elongated, with very oblique suspensorium, extensive 
gape, anteriorly placed orbit, and well marked ethmoidal prominence. The 
sculpture of the cranial roof bones is not exhibited; on the other bones of the 
head it appears to be of a striated character, but it is only distinctly seen in 
the case of the maxilla and mandible. The former has its broad post-orbital 
portion covered with closely set ridges, which pass into an irregular tubercula- 
tion along the dentary margin; the mandible, slender and tapering in shape, 
has also a narrow band of tuberculation along its upper margin, but below this the 
surface is striated with fine ridges, which proceed diagonally from above down- 
wards and forwards, and increase in obliquity from behind forwards. Small 
conical teeth of different sizes may be observed in several specimens. 
The bones of the shoulder girdle present nothing peculiar in their configur- 
ation, and, so far as their external sculpture is visible, it consists of wavy sub- 
parallel ridges. 
The scales of the flank (fig 19) are somewhat large for the size of the fish, and 
are higher than broad, with their posterior inferior angles obtuse; towards the back, 
belly, and tail, they become smaller, and assume the usual rhomboidal shape. 
The articular spine is well marked though small; the keel of the attached 
