EXTINCT BATEACHIA. 



361 



Fig. 



OBVERSE COCTTINUS. 



Such are the characters of a genus whose affinities 

 are interesting but somewhat obscure. The hyoid 

 apparatus is better developed than in any other here 

 described, but it is by no means certain that it was 

 branchiferous at maturity; nor does this character, 

 on the other hand, render it certain that the animal 

 is the larva of one of the other forms here described. 

 The well ossified ribs and vertebras are favorable, 

 though not conclusive, evidence for adult age, while 

 the structure of the hyoid apparatus is more like 

 that of the gilless genera Amphiuma and Protonopsis 

 than it is like the branchiferous genera Siren and 

 Necturus^ or the branchiate young of salamanders. 

 Thus it differs from Proteus in the presence of the 

 first axialhyal and the two first basihyals, and from 

 this genus and Necturus in the possession of four dis- 

 tinct pleural branchihyals. In this it agrees with 

 Amj^hiuma, as it does also with Protonopsis, in the 

 three hsemal branchihyals.* Siren has only two of 



J, 1 jji /., 1 1 ^l^ iii PwirK, premasillary; ma;, max- 



these elements, the first and second, without the iiiiny bone ; mi, mandiwe ; cA', 



.,. 11.11 iixialhval ; h', basal branchi- 



third. As a consequence, m Siren the third and iiyai;7i", (cratohyai;/!'", ?sty- 



, lohyal ; hv, liaBmal branchiliyal; 



fourth pleural elements have no corresponding hae- &', 6", *'". b"", pleural braucM- 

 mal support, an arrangement totally different from 



that of Cocytinus. The arrangement in larval AmUystoma and Triton is 

 quite similar to that in Siren, excepting that in Triton the small basi- 

 hyals are present. 



The question as to whether this genus was 

 in life branchiferous or not is not easily de- 

 cided, since the hyoid apparatus is about 

 equally developed in the branchiferous gen- 

 era Siren and Necturus, and the air-breathers 

 Amphiuma and Protonopsis. Some considera- 

 tions, however, point to an air-breathing type 

 like the last two, though the individual may 

 possibly have been immature. In the gill- 

 bearing genera, as well as in the larva? of Am- 

 phystomx, Tritons, etc., the branchial arches 

 approach nearest to archetypical perfection. 

 Thus in the Siren lacertina (cut 5), two of the 



SIKEN LACEUTIXA. 



« For the nomenclature of these bones I follow Fischer, Ueber die Pemmibranchi- 

 aten und Derotremen, Hamburg, 1864. 



