LABYRINTHODONTS. 197 



cavity for the reception of one of the great tusks. The tooth, indicated 

 by the letter b, is described as exhibiting a pulp-cavity, and the adjoin- 

 ing tooth, c, as showing a new tooth rising into the pulp-cavity, 

 in progress of displacing the old tooth, after the manner of succes- 

 sion in the teeth of the crocodile. PL 63, figs. 2 and 4, repre- 

 sent the fossils on which Prof. Jaeger has founded respectively his 

 species denominated Phytosaurus cubicodon and Phytosanrus cylindri- 

 codon, but it is doubtful whether they are teeth or casts of the sockets of 

 most probably conical teeth, of which they exhibit only the shape 

 of the implanted base : the real teeth that have been discovered 

 in the same quarry as that which yielded the preceding casts have 

 the form represented in fig. 5 : these, like the teeth of Mastodon- 

 saurus Jaegeri, are conical and are marked by fine strise extending 

 from the base to the middle of the crown : they bear the same rela- 

 tive proportions to. the large tusk (PI. 63, fig. 1) as do the serial teeth 

 of the British species of Labyrinthodon to their anterior tusks. (1) 



A third remarkable and characteristic fossil discovered in the 

 Keuper sandstone (alaunschiefer) and described by Prof. Jaeger, (loc. 

 cit. p. 38, pi. V, figs. 1 and 2), consists of the occipital portion of the 

 cranium with two large and separate condyles, as in the batrachian 

 reptiles : on this fossil the Professor founded his species called " Sala- 

 mandrdides giganteus.'\2) Now the teeth of the extinct Batrachians 

 from the New-Red Sandstone in Warwickshire correspond with 

 those of the so-called Mastodonsaurus, in presenting a highly cha- 

 racteristic and pecuhar structure (PL 64 b, fig. 2), which has 

 suggested for the genus to which they belong the name of Labyrin- 

 thodon: and as the great teeth of the so called Mastodonsaurus 

 correspond in size with the cranial fragment with the batrachian 

 condyles above mentioned, it is highly probable that they belong 

 to the same species of reptile as that fragment. But it is cer- 

 tain that the teeth of this gigantic Keuper reptile belong 



(1) The genus Phytosaurus in the Saurian system of H. von Meyer is placed between 

 Mosasaurus and Saurocephalus. I have already proved the latter to belong to the class of fishes, 

 and, if the Phytosaurus be identical with Mastodonsaurus, they must both be expunged from 

 the Saurian order. 



(2) The Salamandro'ides giyanteus of Jaeger, is placed in the system of H. von Meyer, between 

 the Sulamandra (jujantea and the Triton noachicus, in the order Batrachia : it belongs, however, 

 to a distinct family in that order. 



