622 B. F. Kingsbury and H. D. Eeed. 



4. The Operculum develops out of tlie otic capsule of which it 

 appears to be primarily a part. It possesses no stilus but gives 

 attachment to a muscle (M. opercularis). Its morphological position 

 relative to the Columella is caudal and medial. 



5. A Columella only is present in Necturus, Proteus, Crypto- 

 branchus, Amphiuma, ^iren. 



6. In Ambystoma and Chondrotus (Ambystomidse) a Columella 

 is present in the lai*va but it becomes fused with the otic capsule at 

 transformation, and an Operculum is then developed. 



7. A vestigial and fused Columella is found in Salamandra, Triton 

 and Diemictylus (Salamandridse, Pleurodelidse, Cope). 



8. An Operculum is found (in the adult) in the Ambystomidse, 

 Salamandridse, Pleurodelidse. 



9. The Plethodontidse and Desmognathidse possess a single fenes- 

 tral structure bearing a stilus but also giving attachment of the 

 opercular muscle. 



10. Typhlomolge possesses a fenestral plate of plethodontid char- 

 acter. It has a fragmented stilus and lacks the M. opercularis. 



11. The Musculus opercularis is absent in (a) Necturus, Proteus, 

 Cryptobranchus, Amphiuma, Siren, Typhlomolge ; (b) in larvse gen- 

 erally. It is present in the adult Ambystomidse, Salamandridse, 

 Pleurodelidse, Plethodontidse, and Desmognathidse. 



12. The Stilus columellse is distally joined to the Squamosum, 

 Palatoquadratum, Quadratum, singly or in combination. In !N"ec- 

 turus, Proteus, Cryptobranchus, Typhlomolge and larvse generally 

 (Ambystomidse, Plethodontidse, Desmognathidse) it is directly con- 

 nected with the squamosum. 



13. During growth or at transformation the connection tends to 

 shift, usually to the Palatoquadratum. 



14. The stilus is fragmented in Typhlomolge, vestigial in 

 Batracoseps and Siren, absent in Triton and Diemictylus. In Sala- 

 mandra its distal end is fused with the Palatoquadratum. 



15. In development the proton of the Columella appears to be 

 outside the otic capsule in those forms in which its development has 

 been traced (Necturus, Ambystoma, Spelerpes, Plethodon, Crypto- 

 branchus). 



