52 ' TRIASSIC FISHES AND PLANTS. 
thing to the generic description, as they show better than any before known 
the under and upper sides of the head. From these it appears, first, that 
on the under side of the body the scales extend in a V-shaped point consid- 
erably forward of the pectoral fins, the extreme angle being under the center 
of the head. Secondly, the apex of the arch formed by the mandibles is 
occupied by a median jugular plate similar to that of Ama; its surface is 
covered with coarse, rounded, or elongated tubercles, and its sides are notched 
to receive the conical extremities of the interclavicles (?) by which it is bor- 
dered. These are covered with polished raised lines with a radiated arrange- 
ment at the extremity; they are often broken into tubercles of enamel. 
Thirdly, the mandibles are narrow and slender and, like the other bones of 
the head, coarsely granulated. Fourthly, the under side of the pectoral 
fins shows about ten rays which, simple at base, soon divide into polished 
rods articulated only toward their extremities; in this respect showing a 
structure very different from that of the upper surface, in which the articu- 
lations are short and numerous, apparently metamorphosed scales; a chiar- 
acter exhibited throughout the unpaired dorsal, caudal, and anal fins. 
The bones of the sides and top of the head are not quite as distinctly 
shown, but the following points of structure can apparently be made out: 
The cranial bones are all rather coarsely tuberculated; they consist of a 
pair of large polygonal frontals, which are notched on the anterior lower 
border for the eye orbit; the ethmoid is pentagonal, wedge-shaped poste- 
riorly, the point interposed between the diverging lines of the frontals; the 
sides are straight, slightly inclined toward each other forward, the anterior 
margin apparently joining the premaxillaries, which are united to form a 
transversely oval bone bristling with teeth—the extremity of the muzzle. 
The posterior angles of the frontals are cut to receive small oblong or ovoid 
parietals. The middle line of the head terminates behind by a triangular 
supraoccipital, of which the rounded base fits into a sinus in the frontals. 
On either side of the supraoccipital are small, polygonal post temporals, of 
which the posterior edge is joined by the scales of the back. The max- 
illaries are spatulate, broadly rounded or truncated behind and anteriorly 
fitted to the premaxillary. The orbit is formed by a bony ring, but the 
number of pieces composing it is not shown. 
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