ON BRITISH FOSSIL REPTILES. 187 



plate, stamping the fossil with a Batrachian character conspicuous above all 

 the Saurian modifications by which the essential nature of the fossil appears 

 at first sight to be masked. 



In the anterior frontal bone there are indications of Crocodilian structure. 

 Its superior surface is sHghtly convex and pitted with irregular impressions ; 

 and from its posterior and outer part it sends downwards a broad and slightly 

 concave process, which appears to be the anterior boundary of the orbit. This 

 process presents near its upper margin a deep pit, from which a groove is con- 

 tinued forwards ; and in tlie corresponding orbital plate of the Crocodile there 

 is a similar but smaller foramen. 



From these remains of the cranium of the Lah, pachygnathus, it is evident 

 that the facial or maxillary part of the skull was formed in the main after the 

 Crocodilian type, but with well-marked Batrachian modifications in the in- 

 termaxillary and inferior maxillary bones. The most important fact which 

 they show is, that this Sauroid Batrachian had subterminal nostrils, leading to 

 a wide and shallow nasal cavity, separated by a broad and almost continuous 

 palatal flooring f om the cavity of the mouth ; indicating, with their horizon- 

 tal position, that their posterior apertures were placed far behind the anterior 

 or external nostrils; whereas in the air-breathing Batrachia the nasal meatus 

 is short and vertical, and the internal apertures pierce the anterior part of the 

 pjilate. It may be inferred, therefore, that the apparatus for breathing by 

 i-nspiration must have been present in the habyrinthodon as in the Crocodile ; 

 and hence still further, that the skeleton of the Labyrinthodon will be found 

 to be provided with well-developed costal ribs, and not, as in most of the exist- 

 ing Batrachians, with merely rudimentary styles. Since the essential condi- 

 tion of this defective state of the ribs of Batrachians is well known to be their 

 fish-like mode of generation and necessary distension of the abdomen, it is 

 probable that the generative economy of these fossil reptiles, in which the 

 more complete ribs would prevent the excessive enlargement of the ovaria 

 and oviducts, may have been similar to that of Saurian reptiles. 



A fragment of a vertebra of Lab. pachygnathus presents analogous charac- 

 ters to the vertebra of the Lab. leptognathus previously noticed. 



Of the few bones of the extremities whicii have come under my inspection, 

 one presents all the characteristics of the corresponding part of the humerus 

 of a toad or frog, viz. the convex, somewhat transversely extended articular 

 end, the internal longitudinal 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 medullary ca- 

 vity. In its structure as well as in its general form, the present bone agrees 

 with the Batrachian, and differs from the Crocodilian type. 



In the riglit 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 extremity of which is separated from the acetabulum by a smooth con- 

 cave groove, I)oth of which are wanting in the crocodile, there being only a 

 slight rising of the upper border of the acetabulum. These characters, how- 

 ever, 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 i\w. Batrachia anoura ; but it does not attain in the Labyrinthodon the par- 

 allel of the anterior margin of the acetabulum, and the bone terminates in a 

 thick truncated extremity a few lines anterior to tlie acetabidum ; which gives 

 an essential feature of resemblance to the Crocodiles and difference from the 



