578 B. F. Kingsbuiy and H. D. Reed. 



studied ( Gjrinophilus, Pletliodon, Stereochilus, Spelerpes) the con- 

 nection was with the squamosum only. In the adult there is a very 

 wide variation, from a close articulation with the squamosum only (as 

 in Manculus) to an intimate connection of the stilus with a cartila- 

 ginous process of the palatoquadrate, as in Stereochilus, Autodax 

 and Plethodon. The other genera show an intermediate condition ; 

 in Hemidactylium and Spelerpes the connection with the squamosum 

 is the closest, while in Gyrinophilus there is an equally close articula- 

 tion with the subsquamosal process of the quadrate; in no one of them 

 was the cartilaginous process of the palatoquadrate as well developed 

 as in Stereochilus, Autodax, and especially Plethodon. 



The variation in the connections of the distal end of the stilus 

 is undoubtedly associated with the inclination of the suspensorium 

 to the long axis of the skull. During the period of growth, due to 

 the relative displacement of parts, the distal end of the suspensorium 

 is "drawn" forward, bringing its long axis more nearly parallel with 

 that of the skull. 



The definitive fenestra vestibuli of the Plethodontidse is large and 

 lateral in position, more nearly representing the primary fenestra 

 of other urodeles, — a condition recognized by Parker.^ The columella 

 is correspondingly large, nicely filling the opening, and projecting 

 slightly back of it, as presently to be described. The plan of ossifi- 

 cation in the columella is so characteristic that we have come to 

 consider it as the Plethodontid type. 



The M. opercularis, though absent in the larva, is a well devel- 

 oped structure in the adult. It attaches to the caudal portion of 

 the fenestra! plate, which there possesses a decided excavation occu- 

 pied by the tendon of the muscle, giving the "scooped out" appearance 

 noted by Parker. 



^Parker, '82, p. 199. "The under face of this ear capsule (in Spelerpes) is 

 very different from that of most high "Urodelous" skulls. 



"In those massive typical Caducibranch skulls just described, e. g. WotopJi- 

 tJialmus (PI. XVII) and Cj/nops (PI. XVIII), the vestibule is in the form of 

 a smooth bulla, with the stapes set on behind ; and that plate is either quite 

 soft or very slightly ossified ; it is also relatively small. 



"In Spelerpes (PI. XXI, Figs. 2, 3, and PI. XVIII, Fig. 10) the vestibule 

 is but little protuberant ; its fenestra is lateral, and corresponding with the 

 stapes, very large." 



