54 GEOLOGICAL MEMOIRS. 
from, the skull of the 4. minor, which he has more carefully exa- 
mined ; the anterior teeth are more pomted and wider separated. 
than in Labyrinthodon, and the three interior ones are small when 
compared with the large-teeth which appear further back in the latter. 
The anterior frontal bone seems to the reviewer to lie in the same 
place, in which, according to the author, the lachrymal bone occurs 
in Archegosaurus Decheni; it appears as a flat-bone contracting to a 
point in front and with the anterior angle of the orbit forming a 
notch in its posterior extremity, thus perfectly agreemg with the 
Labyrinthodon. This bone always borders immediately on the 
frontal. bone, and outwardly on a longer bone, which, as im the 
Labyrinthodon, is prolonged forwards as far as the region of the 
half-length of the nasal bones, and goes so far back posteriorly, as 
to take part in the formation of the margin of the orbit. In position 
and size this bone corresponds to the lachrymal bone in the Laby- 
rinthodonts, in which, however, the union of the anterior frontal bone 
with the malar bone excludes it from the margin of the orbit. 
The ribs of the Archegosaurus are only known from the impres- 
sions they have left in the stone. These, however, are sharp enough 
to justify the conjecture that the ribs were of an osseous consistence. 
Their form cannot be distinctly recognised ; the processes were broad 
and strong. Of Archegosaurus Decheni seventeen dorsal vertebree - 
(Ruckenwirbel) are preserved ; of A. minor seven short vertebrze, 
referred by the author to the neck, which consequently was half as 
long as the head ; of 4. medius there is a series of nineteen vertebrze 
extending to the pelvis. The ribs are not very long, only slightly 
curved, obtuse at both ends, and rounded in the middle. The broad 
exterior ends of these dorsal ribs were connected with a kind of ribs, 
which were twice as long and only half as thick as the dorsal ribs, 
and at the same time terminated in a point. 
Immediately connected with the skull was an osseous apparatus of 
singular structure, which the author considers to have been the hyoid 
bone (Zungenbein), which would thus be larger than in any other 
animal. This apparatus consists of a flat-arched, central plate of an 
acute rhombic form, to the anterior part of which, on both sides, 
there was attached a wing-shaped process, furnished behind with a 
styliform process. From the reticulated centre of the upper surface 
of the rhombic plate delicate lines radiated, which in the lateral 
wings proceeded rather from the posterior external angle. The 
author believes that this apparatus was prolonged anteriorly into 
a thick point, on which behind, at both sides, two cylindrical pro- 
cesses were attached at right angles, which are regarded as the horns 
of the hyoid bone. The reviewer did not find this part preserved in 
the skull he examined ; he found the other bones, however, the sharp, 
natural outlme of which showed that no part was broken off, and 
hence this anterior part must have formed a separate bone, which is 
perhaps more correctly regarded as the sphenoid bone. The rhombic 
plate would then be the proper body of the hyoid bone, the lateral 
parts on its anterior half the posterior horn, and the styliform pro- 
cess (which the reviewer believes was not anchylosed to the horn), 
