233 REPORT--18r3. 



saurus, and Anthracosmirus. In Lahjrinthodon this longitudinal row 

 terminates in front with a large tusk, which is at the same time the 

 outermost of a short transverse series*. 



In the remarkable genus Batrachiderpetonf a very different type of 

 palatal structure is presented. Here the vomers form a pair of large, 

 somewhat triangular plates, which support the premaxillaries in front, and 

 pass to the pterygoids on either side behind. A large central tract of the 

 vomerine surface is thickly covered with minute conical teetli, while the outer 

 margin of what is apparently the same bone bears a series of ten or more 

 stronger compressed teeth J. The structure here described is most nearly 

 paralleled b}' the Perennibranchiate Amphibia and by certain fishes, the 

 Carboniferous Mec/alichthys among the rest. 



The Premaxillavy. — The premaxillary is usually double in Labyrin- 

 thodonts, but single in Trematosaurus\. Its proportions vary greatly 

 according to age and species. 



On the superior surface of the skull the premaxillary articulates with the 

 nasal and maxillary of the same side, and bounds in jDart the external nasal 

 aperture. On the palatal surface it is supported behind by the vomer and 

 ordinarily by the maxillary also. The row of maxillary teeth is continued 

 along the premaxillary border, in most cases without interniption or marked 

 difference in size. There may be eleven or more premaxillary teeth on each 

 side ; the number is not constant beyond the limits of the species. 



Elliptical cavities have been observed upon the under surface of the 

 premaxillary ; and these have been compared to the dental pits of Alligator 

 by Eurmeister, who supposes that they received the large mandibular teeth ||. 

 This view harmonizes well Avith the structure of Trematosaurus, in which 

 there are large tusks internal to the serial mandibular teeth. In Archego- 

 saurus, however, there are no tusks in the mandible, yet the cavities in the 

 palatal plate of the prasmaxilla are plainly visible. It is possible that these 

 apertures, as well as the similar one in Anthracosaurus, may have been 

 vacuities occupied in the living animal by membrane^. 



The premaxillary of Batraclndeiyeton appears to differ essentially from 

 the bone as it exists in other Labyrinthodonts. It is produced outwards for 

 a short distance beyond the end of the series of teeth, and appears to have 

 terminated in a free point unconnected with a maxilla, as in Mcnohranclms, 

 Siren, and Proteus. 



The Maxilla. — The maxilla in Labyrinthodonts takes the form of a long 

 narrow slip of bone, comprising nearly all the marginal alveoli of the teeth 



* Owen, ' Trans. Geol. Soc' vol. vi. part 2. 



t Hancock and Atthey, ' Nat. Hist. Trans. Northumberland and Durham,' vol. iv. p. 208. 



\ This outer slip, reaching to the pterygoid, is possibly a palatal. 



§ Burmeister, loc. cit. p. 8. " Two premaxillary bones are usually ascribed to the 

 Batrachia ; but in many Salamanders they are confluent. Thus, while they are double in 

 Salamandra, they are single in Hemimlamandra, Triton, and Diemi/cfylns. In Ambly- 

 Btomidffi they are double. Among Plethodontidae they vary. Of Plethodontine genera, 

 Batrachoseps and &tercochila have them single and Plethodon double. Of Spelerpine 

 forms, Manculus, (Ediinis, and Spelayes have but one, and Geofriton and GyrinophUiis 

 have two premaxillaries. Desmognathus and AmpMuma have single promiixillaries." — 

 Prof. E. D. Cope, 'Extinct Batrachia, Eeptilia, and Aves of North America,' p. 4 

 (footnote). 



II Loc. cit. p. 9. See also Prof. Huxley, ' Anat. of Vert. Animals,' p. 183. " In many of 

 the Labyrinthodonts, again, two of the anterior mandibular teeth take on the form of long 

 tusks, which are received into fossEC, or foramina, of the upper jaw, as in most existing 

 Crocodilia." 



^ In the description of Anthracosaurus, Prof. Huxley refers to this cavity ae the 

 anterior palatine foramen. 



