TRIASSIC LABYRINTHODONS. 191 



From this the bone gradually decreases in vertical extent to its broken fore end. 

 In the second and larger fossil (fig. 2) the exterior of the lower three fourths of 

 the bone is strongly sculptured by obtuse interrujDted ridges, mainly radiating 

 from the lower border below the articular surface (fig. 2). The inner side of the 

 ramus (fig. 2) is comparatively smooth, and shows the termination of the depression 

 which lodged the liiud end of the dentary element. Portions of the maxillary bone 

 and teeth of this species are shown in figs. 4, 5, and 6, Plate 4. 



Species — Lahijrinthodon leptognatlms. (Batrachia, Plate 3.) 



Of the fossils referred to the above species the most instructive was the portion 

 of skull represented in figures 1 and 2, of the natural size. Careful removal of 

 the stony matrix exposed, on the palatal surface (fig. 2) a broad divided vomer (h), 

 contributing a somewhat larger proportion to the roof of the mouth, than the 

 divided vomer characteristic of existing Toads and Frogs. The position and rela- 

 tive size of the inner or palatal nostril (c) added to the batrachian characters. 

 Anterior to this part of the palate was the base of a tooth, which, compared with 

 the row of maxillary teeth, might be termed a tusk. The labyrinthic structure 

 was instructively shown in a section of this tooth. So much of the upper wall of 

 the skull is preserved as to show the broad, flattened shape of its facial portion ; 

 but the extent of the maxillary and nasal bones composing the roof presents a 

 marked distinction from the framework of the similarly shaped skidl in existing 

 broad and flat-headed Batrachians. In these the maxillaries have the form of 

 elongate styles, attached by a slightly expanded fore end, and terminating behind 

 in a free point : they are, also, edentulous. 



The outer surface of the broad facial part of the skull of Lahyrinihodon is 

 sculptured in a degree recalling that of the outer surface of the lower jaw of the 

 huge species above described. Irregular grooves and sinuses are divided by 

 corresponding risings. An angular furrow runs nearly parallel with the alveolar 

 process, a little above it, defining it from the broad upper flat surface of the 

 skull ; a second less angular furrow inclines one side as it extends forward. 



The alveolar part of the fossil includes thirty-one sockets, the foremost, lodging 

 the base of a tooth three times the size of the next, which commences the series of 

 smaller teeth, gradually decreasing in size as they extend backwards. A side view 

 of the above- described fossil is given in fig. 3, in which a indicates the tusk of 

 the outer dental series and h that of the vomer. 



The dental character of the present species is more fully shown in the con- 

 siderable proportion of the left mandibular ramus, figured in Batmchia, Plate 4, 



