78 SCIENTIFIC AND LITERARY NOTES. 
same structure which is shown by alike section of a tooth of the Lepidosteus 
oxywrus.* The same principle of dental composition is exemplified in the teeth 
of most of the ganoid fishes of the Carboniferous and Devonian systems, and is 
carried out to a great and beautiful degree of complication in the old red Dendro- 
donts. The repetition of the same principle of dental structure in one of the 
earliest genera of Reptilia, associated with the defect of ossification of the endo- 
skeleton and the excess of ossification in the exa-skeleton of the head, decisively 
illustrate the true affinities and low position in the Reptilian class of the so-ealled 
Archegosauri. For other details of the peculiar and interesting structure of the 
animals representing the earliest or oldest known order of Reptiles, Prof. Qwen 
referred to the article ‘‘ Paleontology” in the ‘ Encyclopedia Britannica.’ This 
order is “‘ carboniferous.”” 
Order 11.—Labyrinthodontia.—Head defended, as in the Ganocephala, by a 
continuous casque of externally sculptured and unusually hard and polished osse- 
ous plates, including the supplementary “ postorbital” and “‘ supertemporal” bones, 
but leaving a “foramen parietale.”’{ Two occipital condyles. WVomer divided and 
dentigerous. Two nostrils. Vertebral centra, as well as arches, ossified, bicon- 
cave. Pleurapophyses of the trunk, long and bent. Teeth rendered complex by 
undulation and side branches of the converging folds of cement, whence the name 
of the order. Osseous scutes in some. The reptiles presenting the above charac- 
ters have been divided, according to minor modifications exemplified by the form 
and proportions of the skull, by the relative position and size of orbital, nasal 
and temporal cavities, d&e., into the several genera; as e.g. Mastodonsaurus. 
Trematosaurus, Metopias, Capitosaurus, Zygosaurus, Xestorrhytias. The relation 
of these remarkable reptiles to the Saurian order has been advocated as being one 
of close and true affinity, chiefly on the character of the extent of ossification of 
the skull and of the outward seulpturing of the cranial bones. But the true nature 
of some of these bones appears to have been overlooked, and the gaze of research 
for analogous structures has been too exclusively upward. If directed downward 
from the Labyrinthodontia to the Ganocephali, and to certain ganoid fishes, it sug- 
gests other conclusions, which had been worked out by Prof. Owen, in his article 
on “ Paleontology,” above referred to. There is nothing in the known structure 
of the so-named Archegosaurus or Mastodonsaurus that truly indicates a belonging 
to the Saurian or Crocodilian-order of reptiles. The exterior ossifications of the 
skull and the ecanine-shaped Jabyrinthic teeth are both examples of the Salaman- 
droid modification of the ganoid type of fishes. The small proportion of the fore- 
limb of the Mystriosaurus in nowise illustrates this alleged saurian affinity; for 
though it be as short as in Archegosaurus, it is as perfectly constructed as in the 
Crocodile, whereas the short fore-limb of Archegosaurus is constructed after the 
simple type of that of the Proteus and Siren. But the futility of this argument 
of the sauroid affinities is made manifest by the proportions of the hind-limb of 
Archegosaurus ; it is as stunted as the fore-limb. In the Labyrinthodonts it pre- 
sented larger proportions, which, however, may be illustrated as naturally by 
these proportions of the limbs in certain Batrachia, as in the Teleosaurus. 
* Wyman, ‘ American Journal of the Natural Sciences,’ October, 1843. 
+ The corresponding vacuity is larger in some ganoid fishes. 
