HYNOBIIDAE. 447 



forms seem adapted to a more aquatic mode of life. A similar process 

 in the more remote past produced the Cryptobranchidac. 



Owing, perhaps, to their dependence on external fertilization, this 

 group seems never to have produced forms adapted to a less aquatic 

 mode of life. In this the Hynobiidae offer a great contrast to the 

 Plethodontidae in which all the forms practise internal fertilization, 

 and in which many or most of the species are terrestrial. 



From a geographic standpoint the inferences to be drawn from the 

 distribution of the Hynobiidae are: that Sakhalin has been connected 

 with the mainland rather than with Yezo; that the Tsugaru Strait is 

 of great age, Yezo having been separated from Hondo for considerable 

 time; that the other islands of Japan have been connected with each 

 other and with Korea both before and after the separation of Yezo ; 

 and that the present Korean Strait is of recent age. 



Before embarking upon a systematic survey of the family it may be 

 well to review briefly the significant features of the anatomy and the 

 variations thereof. 



The prearticular bone is distinct in the lower jaw of Hynobiidae and 

 Cryptobranchidac and fused with the angular in the jaw of all other 

 salamanders. Larvae of Onychodactylus fischcri have a horny edge 

 on the dentary as well as teeth. This structure is seen elsewhere 

 among salamanders only on the dentary of the Sirenidae. 



A free lachrymal, extending from the orbit to the naris, is a feature 

 of all Hynobiid skulls examined by me. (B. sinensis, 0. fischcri, H. 

 leechii, H. per opus, H. kimurai, H. rctardatus, H. vandenburghi). 

 Wiedersheim figures a lachrymal in R. sibiricus and in H. nacvius and 

 mentions its presence in H. kcyscrUngii. But Schlegel figures H. 

 nacvius as without a lachr3 T inal and depicts a similar condition in 0. 

 japonicus, while Okajima failed to find a lachrymal in the latter ani- 

 mal. I can only comment that the bone is hard to see at times, being 

 overlapped by both maxilla and nasal, and underlaid by the pre- 

 frontal. 



In both Hynobiidae and Cryptobranchidac the nasals meet in the 

 middorsal line and the nasal spines of the premaxillae are very short. 

 This is in decided contrast to the condition of these elements in 

 Ambystomidac, Salamandridae, and Plethodontidae, where the nasals 

 are nearly always separated by the long spines of the premaxillae. A 

 large premaxillary fontanelle is present in Onychodactylus: a smaller 

 one in Pachypalaminus, according to a sketch kindly furnished me by 

 Dr. Van Denburgh; and small ones are found in Batrachu perns, and, 

 according to Wiedersheim 's figure, in Ranodon. Except in young H. 



