GANOCEPHALA. 201 



illustrates the true nature and low position in the reptilian 

 class of the so-called Archegosauri. 



Besting upon and protected by the throat-plate in the 

 middle line, there is a longish slender bone, either basi- or 

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

 AmjjMuma and other Perennibranchiates. That two pairs 

 of slender bones projected outward and backward from the 

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

 gosaurus 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 AmpJivwnm, and are cerato-hyals. The shorter 

 posterior pair answer to thebranchi-hyals* in Aw^Muma and 

 other Perennibranchs. There is no such pair in the hyoidean 

 arch of any known Saurian. 



External to the ends of the above lateral elements of the 

 hyoid apparatus, are slightly curved series of dots or points. 

 In the small relative size of these indications of branchial 

 arches, the Archegosatcrus agrees with the Amphiuma. 



No doubt, in the fully-grown Arc7iegosaurus, the lungs 

 would be equal to the performance of the required amount of 

 respiration ; but the retention of such traces of the embryonal 

 water-breathing system in the adult leads to the inference 

 that the animal must have affected a watery medium of exist- 

 ence for as great a proportion of its time as is observed to be 

 the case in the existing perennibranchiate reptiles ; in which, 

 notwithstanding the degree of development of the lungs, the re- 

 spiratory function seems to be mainly performed by the gills. 



The additional marks of affinity to fishes which the Arche- 



* For the meaning of the names of bones, see the writer's works " On the 

 Archetype of the Yertebrata Skeleton," 8vo, 1848 ; " Lectures on Anat. of 

 Fishes," 8vo, 1846; and " Principal Forms of the Skeleton and Teeth," 12mo, 

 1854. 



