176 FOSSIL FISHES OF THE ENGLISH CHALK. 
attains its greatest depth behind, where its sharp postero-superior angle is produced 
into a buttress against the splemial; it then rapidly contracts imto its symphysial 
half, where it is thickened and curves inwards to meet its fellow in a moderately 
stout symphysis (Pl. XXXVII, fig. 7). The oral border of the dentary is rounded 
and toothless, and its outer face is smooth, except quite at the postero-inferior 
angle, where it is slightly tuberculated. Beneath it hes a partially-separate 
tuberculated scale of bone (Pl. XXXVII, fig. 7, «d.), which is probably an 
infradentary reduced in size. Of the meckehan cartilage there are only two 
ossified remnants, one projecting behind the angular at the posterior extremity of 
the jaw (Pl. XXXVII, fig. 5, w.), the other forming a small articular element 
(fig. 6, art.), which is situated inside the upper margin of the angular just within 
its hinder half. The articular appears to be fused with the supporting angular 
bone, and does not exhibit its precise shape; but in an allied genus, Mawsouia, 
from the Lower Cretaceous of Brazil,! it is a separate element and seen to be 
merely a small nodule of bone, large enough to bear the facette for the ginglymoid 
articular end of the quadrate. The inner face of the mandible is formed by a thin, 
flat splenial plate, in which no sutures can be distinguished (Pl. XXXVI, figs. 
1, 5, spl.). Its hinder portion corresponds in shape with the hinder half of the 
angular ; its deepest portion in the middle third has a straight upper edge, while 
its anterior portion contracts forwards inthe same manner as the dentary to which 
it 1s apposed. Its imner or oral face is covered with minute tubercular teeth, 
which become enlarged on the anterior region supported by the buttress of the 
dentary (just visible in Pl. XXXYV, fig. 9). A separate coronoid bone is suturally 
united with the upper edge of the splenial, and is usually displaced in the fossils. 
It is irregularly triangular in shape, with the middle of its antero-superior edge 
thickened, indented, and projecting outwards (Pl. XXXV, fig. 10, cor.), while its 
inner face (Pl. XXXVII, fig. 8) is covered with minute tubercular teeth lke those 
of the splenial. 
Of the hyoid arch only two elements have been seen in the fossils. The 
stylohyal (Pl. XXXVI, fig. 1, sty.) is a long, laterally-compressed lamina of bone, 
truncated at each end, and shehtly constricted in the middle. The ceratohyal, 
partly seen in Pl. XXXVITI, fig. 1 (chy.), is also laterally compressed, but scarcely 
expanded at the ends, and bearing on the middle of its lower edge a thin process 
of bone, which is about twice as wide as deep. 
The branchial arches are conspicuous in many specimens, but their extremities 
have never been clearly observed. They appear to be in four pairs (Pl. XXXVIII, 
fig. 1, br.), each arch consisting of a single curved bone which is deeply grooved 
on its hinder face. They are united below by a large copula of the pecular form 
which is always found in Coelacanth fishes. Its smooth, expanded, bilobate, 
hinder end is well seen in Pl. XXXVII, fig. 9 (cop.). There are no traces of 
1 A. S. Woodward, Quart. Journ. Geol. Soc., vol. lxiii (1907), p. 136 
