178 PALEONTOLOGY 



the teeth of most of the ganoid fishes of the carboniferous and 

 Devonian systems, and is carried out to a great and beautiful 

 degree of complication in the "old red" Dendrodonts. 



The repetition of this structure in the teeth of one of the 

 earliest genera of Reptilia, associated with the defect of ossifi- 

 cation of the enclo-skeleton and the excess of ossification in 

 the exo-skeleton of the head and nape, instructively illustrates 

 the true affinities and low position in the reptilian class of 

 the so-called Arcltcgosauri. 



Besting upon and protected by the throat-plate in the 

 middle line, there is a longish slender bone, which must belong 

 to the median series of the hyoid system, either basi- or uro- 

 hyal ; it is most probably homologous with the uro-hyal of 

 AmpMuma and other Perennibranchiates. That two pairs of 

 slender bones projected outward and backward from the 

 median series, is shown by more than one specimen of Arche- 

 gosav/ms in the British Museum. The anterior pair is the 

 longest ; these are situated as if they had been attached, one 

 to each side of the broad "throat-plate," which may have 

 represented a basi-hyal. The anterior pair are homologous 

 with the corresponding longer pair of appendages to the broad 

 basi-hyal of Amphiuma, and are cerato-hyals. The shorter 

 posterior pair answer to the branchi-hyals in Amphw/ma and 

 other Perennibranchs. There is no such pair in the hyoid; an 

 arch of any known Saurian. 



External to the ends of the above lateral elements of the 

 hyoid apparatus, feeble traces of arched series of bony nuclei 

 were detected by Goldfuss, and interpreted by him as remains 

 of partially ossified branchial arches. In all those specimens 

 possessing them they present the outline of two or three arches 

 in dots, or slightly curved series of dots or points. In the 

 small relative size of these indications of branchial arches, the 

 Archegosawms agrees with the AmpMuma. 



No doubt, in the fully-grown Archegosaurus, t lie lungs 



