July 301 

 1920 J 



DUNN — PACIFIC COAST AMBYSTOMIDAE 



57 



Figure 2. Dorsal view of fore part of 

 the hyobranchial apparatus. 

 O = Otoglossal. B = Basihyal. CH = 

 Ceratohyal. CB = First Ceratobran- 

 chial. 



idae, absence of otoglossal and presence of second epibranchial. 

 While I do not see the necessity of dividing this group of sala- 

 manders into two famihes, it is worth noticing that Rhyacotriton 

 falls with the genus Ambystoma rather than with Ranodon. 



Another character divides these genera into the same two 

 series. Those of the Asiatic group have very small nasal proc- 

 esses of the premaxiilaries which 

 are widely separated on the mid- 

 dorsal line. The American, among 

 them Rhyacotriton, have long and 

 broad nasal processes which meet 

 on the median line. 



The otoglossal cartilage is ring- 

 shaped, but with a broad dorsal 

 expansion of the ring. This is 

 quite unlike any of Cope's figures 

 of hyoids, yet may be derived 

 without difficulty from that of A . 

 tenebrosum [ensatum] or that of A . jeffersonianum. The absence 

 of nasals may be due to arrested development, as this bone ap- 

 pears quite late in the larval life of A. ensatum. 



The otic capsule is nearly closed by a broad expansion of the 

 columella, which is free all round. The projecting end of the 

 columella has a hgamentous attach- 

 ment with the squamosal. There is 

 another small ossification anterior 

 and ventral to the plate — hke part 

 of the columella, and attached to it. 

 This is probably the operculum. 

 From Reed's recent work (Journ. 



Morph., 33, 2, pp. 325-387, 1920) on Figure 3 Lateral vi^ew of the otic 

 f 7 7 7 r-r- J ^ / region. (Sbghtly tilted.) 



the otic bones of Caudata it would Q = Quadrate. Sq = squamosal. 

 ., . -. ,, Pt = Pterygoid. P = Parietal. Pa= 



appear that for some reason the Parasphenoid. c = columella. = 



1 n 1 J X • 1 ii Operculum? Pe = ' Periotio ' ( = 



columella has outstripped the oper- Exoccipitai + Paroccipitai + Pro- 

 culum. This Reed postulated to 



have been the case in Cryptobrandius. Rhyacotriton olympicus 

 spends much of its time in mountain streams, and unquestion- 



