400 Geological Society. 



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 thirteen lines. 

 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 by a 

 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 internal 

 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 vertebrae 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. 



As the fragment of the ilium was discovered in the same quarry 

 as the two fragments of the cranium and the portion of the lower 

 jaws, Mr. Owen thinks they may have belonged to the same animal ; 

 and if so, as the portions of the head correspond in size with those of 

 the head of a crocodile six or seven feet in length, but the acetabu- 



