598 



B. F. Kingsbury and H. D. Reed. 



By comparing Fig. 11 and Fig. 31 (PI. Ill) of Ambystoma 

 and Fig. 50 (PI. VII) of Triton it is evident that this portion 

 of the otic floor corresponds in position to the operculum. It would 

 seem as though at transformation a beginning of operculum forma- 

 tion was made which does not go through to completion. 



^ Parasphen. 



Prom. p. 



Fig. 20. Ampbiuma means, adult. C.p., cavum perilympbaticum ; Para- 

 sphen., OS parasphenoideum ; Prom, p., prominentia perilymphatica. Sg., os 

 squamosum. 



Siren. 



The only material examined was an adult specimen 133 mm. 

 long. The fenestra vestibuli is here, as in some other forms, filled 

 by a single plate which is cartilaginous in our specimen although 

 Cope ('88) states that it is bony in this species. It is elliptic in 

 outline, facing outwards and downwards with a short stilus stand- 

 ing almost vertical to the plate and slight inclination being in a back- 

 ward and downward direction. The connection of the columella 

 with the suspensorium, if it ever existed, has disappeared. The 

 relation of the stilus to the blood vessels and nerves in this region 

 is typical. 



