SIWALIK CROCODILIA, LACERTILIA,\aND OPHIDIA. 3—211 
Of extinct genera Biplocynodon, originally described from the lower miocene of 
France/ but which also occurs in the tertiaries of N. America/ belongs to the 
alligatoroid group, and is distinguished by the enlargement of the third, as well as 
the fourth mandibular tooth. One of the French species (D. gracilisj has been 
recorded by Dr. FilhoF from the upper eocene phosphorites of Quercy. Bottosaurus,'^ 
from the upper cretaceous of N. America, was described merely from a portion of 
the mandible, which likewise indicates an alligatoroid form. Plerodon^ is also from 
N. America, and has a broad, short muzzle and short symphysis, but the writer is 
unacquainted with its full affinities. The following are gharialoid forms {i.e. have a 
long rostrum, and, as far as is known, the splenial entering into the mandibular 
symphysis), Thoraeosaurus,^ from the upper cretaceous, which is readily distin- 
guished by the existence of a prelachrymal vacuity in the cranium (like Teleosaurus), 
and is said by Leidy to present a strong resemblance to the so-called Gharialis 
macrorhynchus^ of the upper cretaceous of France, but has the cranial rostrum 
tapering more gradually, and the teeth stouter, in which respects it approaches 
Tomistoma : the anterior border of the orbit is not prominent. Holops,^ from the same 
formation, has a cranium presenting a great resemblance to that of Thoracosaurus, 
but lacks the prelachrymal vacuity. The supratemporal fossae in the type species 
are equal in size to the orbits, and the anterior border of the latter is not pro- 
minent; in a cranial rostrum provisionally referred by Cope*^ to H. obscurus, the 
premaxillse have scarcely any terminal expansion, and there are interdental pits in 
the maxilla for the tips of the mandibular teeth. In both this genus and Tkoraeo- 
saurus the cervical ribs are aborted. In AT. obscurks the premaxillary fissure is of 
large size. The relations of the nasals to the premaxillae are apparently unknown, 
but if, as is probably the case, they are the same as in Gharialis^ the writer would 
be inclined to doubt the propriety of generically separating the American forms, 
unless it be that the structure of their teeth is a sufficient distinction. Theca- 
champsaP from the miocene of N. America is a gharialoid having the dental series 
interrupted by large caniniform teeth : its rostrum is very long and slender, and 
the maxillary and mandibular teeth appear to have interlocked. The so-called 
MelitosauruSj Owen, from the reputed miocene of Malta has been shown by the 
present writeF^ to be identical with Tomistoma ; that genus being represented in the 
1 Vaillant, ‘Ann. Sci. Geol.’ vol. III. art. 1. p. 41 (1872). 
2 Vids Cope, ‘ Eep. U. S. Geogr. Surv. W. 100th Meridian,’ vol. IV. pt. 2. Palaeontology, p. 60 (1877). 4to. 
3 ‘Ann. Sci. Geol.’ vol. VIII. art. I. p. 264 (1877). 
4 Vide Jjeidy, ‘Smith. Contrih. Know.’ vol. XIV. art. 6. p. 12 (1865), and Cope ‘ Trans. Amer. Phil. Soc.’ vol. XIV. 
art. 1. pp. 61-62 (1870). 5 Vide Cope ‘Trans. Amer. Phil. Soc.’ vol. XIV. art. 1. p. 62 (1870). 
6 Vide Leidy, op. cit. and Cope, op. cit. pp. 61-79. 
7 Cope, op. cit. pp. 67-71 refers this species to Thomcosaurus, hut in the figure given hy Gervais, the lachrymal region is 
so imperfect as apparently to render it impossible to determine whether prelachrymal vacuities were present. 
8 Vide Cope, op. cit. pp. 62, 67-79. 9 Op. cit. p. 77, figs. 19, 20. 
10 Vide Cope, op. cit. pp. 62-65. Five species are recorded in this memoir, hut in only one is any portion of the skull 
known ; this portion consisting of a fragment of the mandibular symphysis, which, however, is not figured. 
11 In a paper read before the Geological Society on November, 18th, 1885, which will be published in the ‘ Quart. Journ. 
Geol. Soc.’ vol. XLII. (1886). 
