THE LOWER COAL-MEASURES. 183 
Comparing the Newcastle specimen with those from the Halifax 
district, the difference in the size of the spines and teeth indicates 
that the Pleuwrodus occurring in the latter was nearly or quite a 
foot in length; and the difference in the form of the teeth (those 
from the Better-bed coal being much more elongated, and not laterally 
expanded like the smaller teeth described by Hancock and Atthey) 
appears to give support to the determination of L. Agassiz that there 
are two species of Plewrodus, and that the subject of this description 
should retain the name of P. affinis, Agassiz. 
That the spines and teeth have not been found connected by 
shagreen in the Bone-bed will be easily understood when it is con- 
sidered that the remains of much more bony fishes, such as Mega- 
lichthys or Ccelacanthus, are rarely found connected together, and 
that the spines and other hard parts are frequently broken and 
fragmentary. The circumstances attending this deposition indicate 
a shallow littoral area much disturbed by waves and currents. 
Pleurodus, being entirely cartilaginous, would have a very poor chance 
of being preserved in a perfect and connected condition, the soft 
cartilaginous parts quickly decomposing, and the teeth and spines 
becoming scattered by the waves. 
Since writing the above description, I have found, in the cabinet of 
my friend Mr. W. P. Sladen, a very fine and large specimen of the 
spine of Plewrodus (fig. 9); and although it is not from the Bone- 
bed, it may be well to mention it at the present time. In all essential 
particulars it answers to the description already given of the fin- 
ray of Pleurodus affinis, except in its large size. Its length is three 
inches, and its breadth seven tenths of an inch. The point and a 
part of the base are broken off, so that had the spine been perfect, 
it could not have been less than 3-7 inches long. It was found 
above the Black-bed coal at Dudley Hill, near Bradford, Yorkshire. 
HopLoncnus ELEGANS, n. gen. et sp. (PI. X. figs. 12-14.) 
Hight more or less perfect specimens of this Tehthyodorulite, 
besides a few fragmentary ones, have been found and are at present 
in my collection. The genus is enumerated in the list of fossil fish 
occurring in the Bone-bed above the Better-bed coal in the paper 
already referred to, and to it I then applied the name of Hoplonchus. 
Four of the specimens are larger, stronger, and straighter than 
the remaining four, the latter being much curved and more rapidly 
converging to a fine point. The larger spines (figs. 13, 14) are 
about 1:5 inch in length; of this, 1:1 was exposed, and the 
remaining ‘4 inch formed the base, which was imbedded in the 
inteeument of the fish. The line dividing the two parts forms a 
curve from the dorsal margin towards the base at an angle of about 
60° to the length of the spine. The greatest breadth is *2 inch 
at the junction of the basal and exposed part ; from this point the 
breadth gradually diminishes to the apex; the anterior face is nearly 
straight, the posterior slightly curved. The fin-ray is laterally com- 
pressed, and ornamented by a slightly varying number of longitudinal 
Striations ; midway between the apex and the basal line they number 
02 
