14 GEOLOGICAL MEMOIRS. 
This skull, with other remains of the Archegosaurus discovered in 
the interval, was laid before the meeting of the German naturalists 
at Aix la Chapelle, where the reviewer had an opportunity of inspect- 
ing them. This examination, though only cursory, convinced him 
that im this case we had less to do with an animal resembling the 
crocodile than with one most nearly allied to the Labyrinthodonts of 
the Trias. His remarks on that occasion induced the author likewise 
to compare these animals with Labyrimthodon. 
Since the discovery of the Pterodactyle, probably no event in the 
domain of paleontology has been more important than the discovery 
of the Archegosaurus. The author describes this genus in the 
thorough manner that characterizes all his works. Three species, 
Archegosaurus Decheni, A. medius and A. minor, are distinguished. 
The skull of the first species and the portions of its trunk which 
have been found, seem to have belonged to an animal three feet six 
inches long, so that even this, the largest species, was much smaller 
than the Labyrinthodonts of the Trias. 
The determination of the limits of the various bones of the skull 
is associated with many difficulties, as the reviewer has repeatedly 
convinced himself by the examination of a skull presented to him by 
M. Schnur of Treves. The surface of the bones is only preserved in 
the region of the forehead, and there has been covered with lancet- — 
shaped, scale-like elevations and depressions, contrasting very remark- 
ably with the Labyrinthodonts of the Trias, in which the surface of 
the bones of the skull appears, as it were, covered with carved-out, 
small pits and furrows. In the Archegosaurus the anterior angle of 
the orbit of the eye lies nearly in the middle of the length of the 
skull. Comparmg it with the Labyrimthodon, we find that this 
angle in Mastodonsaurus is placed rather more forwards ; in Metopias 
the orbit falls entirely in the anterior, in Capitosaurus in the posterior 
half. The nostrils show nothing of much consequence. In 4. De- 
cheni the long, small, nasal bone, enclosed im the upper maxillary ; 
the upper maxillary indented behind for the reception of the malar 
bone (Jochbein) ; the small size and the position of the lachrymal 
bone and the anterior frontal bone, as well as the form of the parietal 
bone, have little agreement with those of the Labyrinthodonts of the 
Trias, in which the reviewer could never find ‘‘ that the parietal bone 
contributed to form the margin of the orbit,” which, according to 
the author’s view, was the case with the Archegosaurus; m the 
Labyrinthodon the parietal bone is rather prevented from taking 
part in forming this margin by the posterior frontal bone. In Arche- 
gosaurus a bone lyimg more outwards and bordering on the malar 
bone is considered the posterior frontal bone, which the reviewer 
marks on the skull of the Labyrinthodon as ‘ posterior orbital bone’ 
(hinteres Augenhihlenbein), but which the author denies to the Arche- 
gosaurus. If, however, we conceive the posterior frontal bone sepa- 
rated from the parietal bone, as the author assumes, then the form 
and position of the latter bone is not only more correct, but we also 
obtain a posterior orbital bone, and m the same place too where it is 
found in the Labyrinthodon. The reviewer, however, cannot con- 
