395 
and necessary distension of the abdomen, Mr. Owen likewise 
directs attention to the probability that the generative economy of 
these fossil reptiles may ee been similar to that of existing cro- 
codiles. 
A fragment of a vertebrh presents analogous characters to the 
vertebra of the L. leptognathus previously noticed. 
Of the few bones of the extremities which have come under Mr. 
Owen’s inspection, one presents all the characteristics of the corre- 
sponding part of the humerus of a toad or frog, viz. the convex, 
somewhat transversely extended articular end, the internal longi- 
tudinal depression, and the well-developed deltoid ridge. The length 
of the fragment is two inches, and the breadth is oetiee lites: 
The ridges are moderately thick and compact, with a central medul- 
lary cavity: In its structure as well as in its general form, the 
present bone agrees with the Batrachian, and differs from the Croco- 
dilian type. 
Again, in the right ilium, about six’ inches in length, and in the 
acetabulum, there is a combination of Crocodilian and Batrachian 
characters. The acetabular cavity is bounded on its upper part bya 
produced and sharp ridge as in the frog, and not emarginate at its 
anterior part, as in the crocodile. Above the acetabulum in the frog 
the ilium gives off a broad and depressed process, the lower ex- 
tremity of which is separated from the acetabulum by a smooth con- 
cave groove, both of which are wanting in the crocodile, there being 
only a slight rising of the upper border of the acetabulum. ‘These 
characters, however, are well developed in the Labyrinthodon: but the 
process, instead of being depressed is compressed, and its mternal 
extremity is pointed and bent forwards, representing the rudiment 
of the long anterior process of the ilium in the Batrachia anoura ; 
but it does not attain in the Labyrinthodon the parallel of the an- 
terior margin of the acetabulum, and the bone terminates in a 
thick truncated extremity a few lines anterior to the acetabulum ; 
an essential feature of resemblance to the Crocodiles and difference 
from the Batrachians. But the most marked difference in this fossil 
from the crocodile is the length of the ilium posterior to the aceta- 
bulum, in which it agrees with the analogous portion of the frog 
and other tailless Batrachia; while, on the contrary, there is an 
agreement with the Crocodilian type in the mode of articulation to 
the vertebral column. In the frog a transverse process of a single 
vertebra abuts against the anterior extremity of the produced ilium. 
In the crocodile the transverse processes of two vertebre are thick- 
ened and expanded, and joined to a rough, concave, articular surface 
occupying the inner side of the ilium, ‘and a little posterior to the 
acetabular cavity. In the Labyrinthodon is a similar well-marked, 
rough, elongated, concave, articular surface, divided by a non-arti- 
cular surface, and destined for the reception of the external extremi- 
ties of two sacral ribs. The Labyrinthodon likewise agrees with 
the crocodile in the lower part of the acetabulum being completed 
by the upper extremity of the pubis, the anterior and inferior part 
of the ilium offering an obtuse process at the posterior part of the 
lower boundary of the acetabular cavity. 
