OF TRISTICHOPTERUS ALATUS. 385 
while opposite these two dorsals are respectively placed the ventrals and the 
anal. The lower lobe of the very peculiarly shaped caudal fin commences at 
81 inches from the front, and on the dorsal aspect the rays of the upper lobe 
begin to be apparent a few lines further back. 
Another specimen, crushed vertically, and lying on its back,—or more 
correctly, the counterpart of a specimen in that position, is also very nearly 
entire; the front and a considerable part of the right side of the head being 
unfortunately cut off by the edge of the slab, and the extremity of the tail 
being rather distorted and indistinct. If we add half an inch to complete the 
head in front, the length of this example would also be about 10 inches; the 
pectorals arising 21 inches, the ventrals 6 inches, and the anals 7} inches from 
the supposed extremity of the snout. 
These two specimens thus closely correspond with each other, and with the 
more complete of the two examples figured by Sir Pattie EcErton, and show 
the accuracy with which he allowed for its missing portions. Some of the 
more fragmentary specimens before me show, however, that the fish must 
sometimes have attained a considerably larger size, one head measuring, from 
the tip of the snout to the hinder margin of the gill cover, no less than 3} 
inches, which would give over 15 for the entire length of the fish. 
The Head.—The head was protected above by a cranial “buckler” (Plate 
XXXII. figs. 1 and 2, C.B.), which in the leading features of its configuration 
recalls to our minds that of the Sawrodipterini, though its external sculpturing is 
very different. As in that family, it tends to divide across into two portions,— 
a posterior or parietal, and an anterior or fronto-ethmoidal ; here, however, the 
anterior moiety is the longer, exceeding the other by nearly } of its length. The 
hinder division of this buckler is on the whole quadrate in form, but broader 
behind than in front, the posterior and wider margin being also somewhat con- 
cavely excavated. The front portion forms anteriorly a rounded depressed snout, 
and seems on each side to be excavated to take part in the formation of the 
upper boundary of the orbit, though this part of the margin is not so clearly 
defined as might be wished; nor are the nasal openings seen in any of the 
specimens, which is not strange, taking into account their position in Osteolepis 
vet OY 
and Diplopterus, so close to the margin of the upper lip. It is not possible to 
map out the ossifications entering into the composition of this buckler; probably 
their arrangement would not depart much from that which is to some extent 
traceable in the Saurodipterint. As far as the anterior portion is concerned, 
the impression of two distinct /rontals, entering largely into its composition, is 
distinctly seen in the specimen represented in fig. 2, and the presence of a small 
| conical tooth on the labial margin of the snout in another (fig. 1), leads us to 
conclude that the premaxillary (p. mx) was also here represented. The entire 
outer surface of the buckler, as indeed of all the external bones of the head, 
