ON THE CLASSIFICATION OF THE LABYRINTHODONTS. “155 
Pachygonia, Huxley. 
The mandible upon which the above genus is founded presents the following 
peculiarities :—The external surface is strongly sculptured, and has mucous canals 
similar to those of Mastodonsaurus. “The outer wall of the ramus swells out, sud- 
denly, just behind the level of the articular cavity, and the upper edge of the supra- 
angular process is, as it were, bent in by the development of this projection.” ‘The 
outer surface of the postarticular process is clearly more convex than usual, but we 
fail to detect in the text or woodcut of Prof. Huxley’s memoir any really important 
difference between this part of the jaw of Pachygonia and the same part in Masto- 
donsaurus.” The splenial plate (of the articular bone) “exhibits minute, round, 
crater-like elevations.” Teeth transversely oval at the base, conical above, small, 
regular; 16 or 16 only, in the back part of the ramus, are known. 
Measurements (from Prof. Huxley’s Memoir). 
in. 
Greatest depth of mandible. .......... ccc cece cleeencnes (about) 875 
Transverse diameter of mandibular teeth ............0c.e- sees ‘1 
Longitudinal diameter of mandibular teeth.............. (about) 035 
P. iwcurvaTa, Huxley. 
Locality. Panchet Rocks (Triassic ?), Ranigunj, Bengal. 
References. Huxley, Paleeontologia Indica: Part [V. On Vertebrate Fossils from 
the Panchet Rocks, p. 6, figs. 1, 2 [1865]. 
Trematosaurus, Braun. 
Skull (figure). Elongate-triangular, with rounded apex; superior surface flattish, 
concave along the middle line. Orbits. Small, oval, separated by about twice the 
transverse diameter of one of them; margin slightly raised. Palatine foramina. 
Large, closely approximated, semielliptical, the straight sides being adjacent. 
External nasal foramina. Large, elongate-oval, separated by about twice the width 
of one of them. Choane. Elongate-oval, distant. Zeeth (disposition). Premaxil- 
lary 12 to 14, the central ones larger; maxillary numerous, small, nearly uniform ; 
palato-vomerine, two tusks in front of the choana; behind, the teeth gradually 
diminish from large tusks to the ordinary size of maxillary teeth; there are four 
small teeth internal to the choana; mandibular, outer series numerous, uniform, one 
or more tusks forming a short inner row close to the symphysis. Teeth (structure). 
Elliptical in section at the base, conical above, slightly recurved, striate ; internal 
structure similar to that of Mastodonsaurus. Mandibular articulation. The articular 
surface is produced inwards beyond the plane of the ramus, but the nature of the 
supporting mass is not known; a well-developed postarticular process. Cranéal 
sculpture. The centre of each ossification is strongly pitted, and the margin radiately 
sculptured. Thoracic plates. The median plate resembles a Latin cross, with the 
entering and salient angles rounded ; the short (posterior) arm is radiately sculptured 
on the exposed surface ; the rest of the plate is nearly smooth; the lateral plate 
has a thickened and reflected external margin, a short, notched posterior side, and 
a tapering anterior extremity. The sculpture is not known, but doubtless radiated 
from the thickened postero-external angle. 
T. Braunu, Burmeister. 
Orbits central. Palatine foramina narrowed to an acute angle, especially 
in front. 
Locality. Bunter Sandstone of Bernburg. 
References. Braun, Bericht der deutschen Naturforscher und Aerzte, Braunschweig, 
1841, pp. 74, 75 [1842 ].—Zd. Jahrbuch fiir Mineralogie, 1844, p. 569.—Von 
Meyer, Daltentolngte tirttembergs, pp. 4, 6, 7 [1844].—Burmeister, Die 
Labyrinthodonten aus dem bunten Sandstein von Bernburg. I. Tremato- 
saurus [1849].—Von Meyer, Saurier des Muschelkalkes, p. 189, t. 1xi. 
figs. 11, 12 [1847-55).—Jd. Reptilien aus der Steinkohlenformation in 
Deutschland, pp. 111, 112 [1858}. 
