62 THE AMERICAN NATURALIST. [VOL. XXXIX. 
distinct element, the existence of which has been noted, although 
no name has been given it, by later writers. The problem is to 
homologize these elements with those found in the lower jaw of 
other reptiles, in some of which Baur believed that he had dis- 
covered a distinct bone which he has called the presplenial. 
In the mosasaurs (Fig. 3) the matter is simple. Here derm- 
articular (da) and articular (4) have united into a single bone, 
the anterior splint of which occupies exactly the position, — 
below the jaw behind, rising to its inner surface in front,— that 
the dermarticulare does in the Sceloporus embryo. The splenial 
(s) is greatly enlarged and extends far forward on the inner sur- 
face. The other bones call for no comment, except that the 
surangular (s. an) bends inwards over the meckelian in the way 
` described for the lizard. 
Baur begins his account with a description of the turtle 
Emydura (Fig. 4) in which he recognizes his presplenial, but I 
am compelled to think that here he has fallen into error. On 
the inner side of the articular (a) is a long splint-like bone which 
passes forward and upward on the inner side of the jaw (da). 
This Baur interprets as the angular. In its position it clearly 
corresponds to the dermarticulare which has failed to fuse with 
the articulare proper. Below this is a bone as evidently the 
angulare (av) but which Baur is compelled to call the splenial. 
Hence, according to him, the true splenial (s) which occupies 
the same position as in the lizard, is an additional element, the 
presplenial. Baur's mistake! thus had its foundation in his 
identification of the dermarticulare as the angulare although he 
expressly recognizes the fact that in the Lacertilia the articulare 
is composed of chondrogenous and dermal elements. 
In the ordinary turtles, of which the snapping turtle 
(Chelydra) may be taken as an example (Fig. 5), the splenial 
is lacking, the angulare (az) extends back to near the posterior 
end of the jaw, while the dermarticulare (da) forms a very large 
plate on the inner surface, reaching forward to just beneath the 
coronoid process (c). 
Baur has also described and figured the jaw in Sphenodon 
' Baur merely repeats the wrong identification of Cuvier. 
