6 FOSSIL REPTILIA OF THE 
Species—PLIOSAURUS BRACHYDEIRUS, Owen (?). 
In the Museum of Geology at Oxford are considerable proportions of the upper and 
lower jaws of a Pliosaurus from the Kimmeridge Clay at Market-Raisin.* The teeth, in 
number, proportions, and arrangement, correspond so closely with those in the specimen 
above described as to induce me to believe them to belong to the same species. The 
following are the differences which I have noted between them: the widest diastema 
divides the fourth upper tooth from the fifth m the Oxford specimen, not the fifth from 
the sixth: the maxillo-premaxillary suture with the lateral compression at this interval, 
as in the British Museum specimen. If the pair of small anterior sockets and teeth are 
wanting, either through age or accident, m the Oxford specimen the difference noted 
would be accounted for. It may be remarked that the number of alveoli—twenty-six— 
on the least imperfect side of the upper jaw is the same in both skulls, and in both a small 
part of the series is wanting posteriorly. In both the premaxillary part of the jaw con- 
taming four pairs of large teeth is slightly expanded. In the maxillary part of the 
Oxford specimen the teeth increase in size to the sixth; in the British Museum specimen 
to the fifth ; beyond which they gradually diminish. ‘The length of the best-preserved 
alveolar series is 3 feet in the Oxford specimen, and 3 feet 7 inches in that in the British 
Museum. 
In the mandible from Market-Raisin there are thirty-five sockets in each side ; in that 
from Kimmeridge there are only thirty : but as neither specimens have the alveolar series 
quite complete, I do not feel that there is sufficient ground to reject the hypothesis of 
individual variety. In all the essential characters, including length of symphysis mandi- 
bule, the Market-Raisin skull agrees with that in the Kimmeridge example of Phosaurus 
grandis, and differs from that of Pliosaurus trochanterius, about to be described. If, 
however, the minor differences which have been noted between the Oxford specimen 
and that figured in Pls. I and II, should prove to be constant, the specific name 
“ brachydeirus,’ by which I originally indicated Dr. Buckland’s magnificent. speciment 
from Market-Raisin, might be retained for it. 
* “Second Report on British Fossil Reptiles,’ “Report of British Association,” p. 61, 1841. 
+ ‘Odontography,’ p. 283. 
