976 The American Naturalist. [November, 
The teeth of both the inner and outer rows are separated by consider- 
able spaces from each other and are less crowded than in the Labyrin- 
thodonts. 
The outer side of the lower jaw of Archegosaurus decheni is figured. 
It consists of four sculptured bones. Following E. Fraas,? he names 
the upper element outside of the articular. face, the articular, but he 
doubts whether it belongs to the endoskeleton. This element is the 
supranngular, the angular is correctly determined, and the “ infra- 
dentale ” is one of the splenials.* 
The vertebral Column.—There are said to be 25 presacral, one sacral 
and over one hundred caudal vertebrae. Jackel believes that there is 
uncertainty about the morphology of the vertebral column of the Stego- 
cephalia and the higher vertebrata 
Among the Rachitomi he distinguishes four elements: 1. The 
paired upper arches [neural arches Baur] which in Archegosaurus 
unite dorsally into a spinous process [neurapophysis Baur]; 2. The 
paired upper Pleurocentra (Interdorsalia Gadow), which are intercal- 
ated between the upper ends of the Hypocentra; 3. The paired lower 
Pleurocentra, which in the tail separate themselves from the upper Pleuro- 
centra, (Interventralia Gadow, Hypocentra pleuralia). 4. The unpaired 
Hypocentrum which in the tail may split into two centres of ossifica- 
tions. 
First I may mention that the name Intercentrum, first introduced by 
Cope,‘ antedates Gaudry’s’ name Hypocentrum five years. 
Cope says “ The basal portions of the chevron bones are continued 
throughout the greater part of the Vertebral column in the Permian 
Genera Clepsydrops, Metarmosaurus and Epicordylus [Eryops], form- 
ing intervertebral elements to which I have given the name intercentra ” 
— The free elements of the cervical series of some reptiles are prob- 
ably the same.” 
The name Pleurocentrum was introduced by Gaudry* in 1879 ; in the 
*Fraas, Eberhard, Die eager or der Schwebischen Trias. Palæonto- 
graphica Bd. XXXVI, p. 73, Aug. 2 
? Baur, G. Uber die Moralee. A Unterkiefers der Reptilien. Mit 4, Ab- 
Micmnpen Anat. Anz. Bd., XI, Nr, 13, Dec. 21, 1895, p. 410-415. 
a The Homology of the Chevron Bones. AMER, NATURALIST, 
May, 1875, p. 319 ( Published, April 22d). 
audry, Albert. Les Enchainments du Monde Animale dans les Temps 
Géologiques Fossiles Primaires. Paris, 1883, p. 273, fig. 273, A. B- C. 
*Gaudry, Albert. Les Reptiles de l'époque permienne aux environs d'Autun. 
Bull. Soc. Géol. d. France. (3) Tome VII, 1878-1879, Paris, 1879, p. 68, and 
p- 65 in explanation of fig. 7. 
