292 



MK. R. LYDEKKER ON TWO 



the oral surface, on a reduced scale in Plate XII. fig. 2. The outer 

 surface of the bone is ornamented with a coarsely reticulate and 

 ridged sculpture, while the broken teeth show the labyrinthic 

 internal structure characteristic of the Labyrinthodonts ; so that 

 there is no hesitation in referring the si)ecimen to that group of 

 Amphibians. The unfigured articular region is fairly well pre- 

 served, and shows that there was no postarticular process behind 

 the glenoid cavity — a feature in which this jaw agrees with that of 

 the North-American genus Eryojys and the European jLo.ro?W92a. In 

 the dentary bone the bases of twenty-five teeth now remain, these 

 bases having an ovoid section, with the longer diameter at right 

 angles to the axis of the jaw. Externally to this row of teeth 

 there is a well-marked bony parapet, forming the summit of this 

 border of the jaw. The most remarkable feature displayed by the 

 specimen is, however, the presence of a narrow band of about half 

 an inch in width, situated on the bone of the jaw, immediately on 

 the inner side of the alveolar area, and covered with a number of 

 minute knob-like denticles, much resembling in appearance the 

 so-called " shagreen" of the Elasmobranchiate fishes. Apparently 

 this band of denticles stopped short of the symphysial region. 

 Each denticle presents the appearance of a veritable tooth, having 

 a distinct pulp-cavity. 



The intercentrum, already referred to, is figured of the full 

 dimensions in Plate XII. figs. 3, 4. This bone presents the horse- 

 shoe-like form characteristic of the "rhachitomous" Labyrintho- 

 donts, and shows the presence of a distinct facet (a) for the articu- 

 lation of the capitulum of the rib. The absence of ossification in 

 the axial region of the bone shows that it belongs to a Labyrintho- 

 dont and not to an Anomodont, since in the latter group the 

 intercentra always form complete wedges. This is confirmed by the 

 presence of a rib-facet ; since the only known Anomodont with an 

 intercentral costal articulation is the American genus BmboIop7io7nis. 

 I may tal^e this opportunity of mentioning that the evidence 

 appears to be absolutely conclusive as to the correctness of Prof, 

 Cope's identification of the Labyrinthodont intercentrum (hypo- 

 centrum of Gaudry) with the Anomodont intercentrum, as may be 

 verified by a comparison of specimens of the vertebral column 

 of the Labyrinthodont Erijops and the Anomodont Emholopliorus, 

 acquired a few years ago by the British Museum. 



With regard to the afiinities of the form indicated by these two 

 specimens, it may be observed, in the first place, that the only 

 Labyrinthodont hitherto described from the Karoo system, which 

 can be compared in point of size to the present form is the 

 imperfect skull described and figured by Sir R. Owen in the 

 Society^s ' Journal ' * under the name of Bhytidostevs cajyensis. 

 Assuming that specimen to be adult, the superior size of the 

 mandible under consideration would of itself indicate the specific 

 distinctness of its owner from 11. capensis. A comparison shows, 



* Vol. xl. p. 033, pi. x\ii. (1884). 



