396 Geological Society. 



most common disposition of the palatal teeth is a transverse row 

 placed at the anterior part of the divided vomer in Frogs, the Meno- 

 pome and gigantic Salamander, and at the posterior part in certain 

 toads. In the Amphiume*, on the contrary, the palatal teeth form a 

 nearly longitudinal series along the outer margin of the palatine 

 bones. The Labyrinthodon, as already shown, combines both these 

 dispositions of the palatal teeth. The posterior palatine apertures 

 are more completely circumscribed by bone than in most Batrachi- 

 ans, occupying the same relative position as in the Iguana. The 

 posterior margin only of one of the anterior apertures is exhibited 

 in this specimen, but from its curve Mr. Owen infers that the two 

 apertures were not confluent, as in the Crocodile, the Frcg, or the 

 Menopome, but that they were distant, as in the Iguana. 



From the physiological condition of the nasal cavity Mr. Owen 

 is disposed to believe that the Labyrinthodon differed from the Ba- 

 trachians and resembled the Saurians, in having distinct posterior 

 nasal apertures surrounded by bone, and that its mode of respiration 

 was the same as in the higher air-breathing reptiles. In the shed- 

 ding and renewal of the maxillary and the transverse palatal teeth, 

 Mr. Owen shows that the process took place alternately in each 

 row, as in many fishes, whereby the dental series is always kept in 

 an efficient state. 



The author then describes a portion, sixteen inches long, of the 

 left ramus of an under jaw from the Warwick sandstone, and con- 

 sidered to belong to the same species as the bone just described. It 

 is slender and straight, and the symphysial extremity is abruptly 

 bent inwards, and it presents, Mr. Owen says, almost as striking a 

 Batrachian character as any of the bones just mentioned. The an- 

 gular piece is of great breadth, extending on both sides of the jaw, 

 and is continued forward to near the symphysis, forming the whole 

 of the inferior part of the jaw, and extending upon the inner as far 

 as upon the outer side of the ramus, the inner plate performing the 

 function of the detached os operculare in the jaw of Saurians. The 

 dentary bone is supported upon a deep and wide groove along the 

 upper surface of the angular piece, which also projects beyond the 

 groove, so as to form a strong convex ridge on the external side of 

 the jaw, below the dentary piece. This character, which in the 

 large bull- frog (Rana pipiens) is confined to the posterior part of the 

 maxillary ramus, is in the Labyrinthodon continued to near the an- 

 terior extremity. The teeth are long and slender, gradually dimi- 

 nishing in size towards the anterior portion of the jaw, and the 

 fragment presents a linear series of not less than fifty sockets, placed 

 alternately a little more internally ; and at the anterior inflected 

 part of the jaw is the base of the socket of a large tooth. The an- 

 terior portion of the jaw being broken off, it is uncertain if the serial 

 teeth were continued externally to the anterior tusk, a remarkable 

 ichthyic character noticed in another species of Labyrinthodon. 



The sockets of the teeth are shallower than in the upper jaw ; the 



[• Dr. Harlan's dissection of the Amphiuma means will be found in 

 Phil. Mag., First Series, vol. lxiii. p. 325.— Edit.] 



