PROF. OWEN ON THE ENDOTHIODONT REPTILIA. 563 
in that order, resembles the Oudenodonts in the absence of the parial 
ridges projecting from the fore part of the roof of the premaxillary 
palatine vault; also in the presence of a caniniform process on each 
side of the alveolar border of the upper jaw, and in the tuberous pro- 
minence of the nasal bones above the nostrils—a character which is 
present in Oudenodon prognathus (tom. cit. pl. 1x1. fig. 1, 15, “the super- 
narial tuberosity is relatively large,” p.59). In Oudenodon magnus 
also “a low protuberance of the nasal (pl. liv., 15) overhangs part 
of the nostril” (p. 56). The anteriorly contracted orbit, in the 
vertical direction, notable in both species of Endothiodon, is charac- 
teristic also of Oudenodon prognathus (tom. cit. pl. Lxi. fig. 1, 0). 
In both species of Endothiodon the skull is relatively more pro- 
duced anterior to the orbits than in most other Anomodonts: the 
nostrils are more advanced, and both the premaxillary and the maxil~ 
lary bones contribute to the formation of the caniniform process. 
In connexion with this difference we find agreater relative antero- 
posterior extent of the nasal bones, and the occurrence of a pseudo- 
narial opening between the nasal and postfrontal bones. 
Dicynodon, the type of the order Anomodontia, shows a marked 
modification of the reptilian structure in the reduction of the dental 
system to the single pair of upper canines. In Oudenodon this 
modification is carried to the Chelonian extreme of an entire loss of 
teeth ; but the cranial characters are Anomodont, not Chelonian. 
Both Oudenodon and Endothiodon indicate a derivation from 
Dicynodon by the caniniform processes of the upper jaw, although 
all trace of tooth and socket is obliterated in the numerous specimens 
which I have subjected to examination. The combination of two 
bones in the formation of this process in Hndothiodon is signifi- 
cant of its original edentulous condition in that genus, especially as 
the premaxillary constitutes the larger proportion of the process. 
In Oudenodon the process is exclusively formed by the maxillary. 
With the above-cited evidence of adherence to the Anomodont 
type of reptilian skull, I regard the development of teeth internal to 
the alveolar margins of both upper and lower jaws as a character of 
family value in the order. The single row of palatal teeth in Hndo- 
thiodon uniseries recalls the outer row of small teeth in Placodus 
gigas, Agassiz, and Placodus Andriani, Minster. The development 
of the premaxillaries along the upper and fore part of the skull and 
the position of the nostrils are also resemblances of the anomalous 
Muschelkalk reptile to the Anomodonts of the Cape Trias. The 
dental characteristics of Hndothiodon, as of Placcdus, doubtless related 
to the crushing for food of contemporary testaceous and crustaceous 
Invertebrates. 
The palatal teeth in Batrachiderpeton lincatum, Hancock and 
Atthey, closely resemble in size and disposition those of Hndothiodon 
uniseries; but in the Labyrinthodont from the Coal-shale they are 
associated with both premaxillary and vomerine teeth*. It is 
interesting to trace, however, the continuance of a common ichthyic 
* ‘Natural History Transactions of Northumberland and Durham,’ yol. iy. 
plate iy. fig. 2, 2. 
