31 



burrowiug in the ground. He says it has been known to burrow in soft 

 ground to the depth of three feet. 



Family V. PLETHODONTID^. 



(Includes Prof . Cope's families Plethodontidce, Desmognathidoe, and Thoriidce,^ 



51, 33). 



Body salamandriue in form. No persistent gills or gill-slits. Verte- 

 brje amphicoelous or opisthoeoelous. Teeth on posterior edge of vomers. 

 Parasphenoidal teeth present. Tongue extensively free on sides or all 

 round. Carpus and tarsus cartilaginous. 



Key to the Subfamilies of Plethodontidce.^ 



A. Vertebrae amphicoelous. Plethodontinoi, p. 31. 



AA. Vertebrae opisthoeoelous. 



a. Carpus and tarsus cartilaginous. Desmognathinm, p. 42. 



aa. Carpus and tarsus osseous. Extralimital. Thmiince. 



Subfamily PLETHODONTIN^. 

 Vertebrse amphicoelian. Carpus and tarsus cartilaginous. 



Key to the N. A. Genera of Plethodontince. 



A. Tongue free along the sides, but not in front, 

 a. Posterior digits 4. 



b. Costal grooves 18-31 ; Pacific States. Batrachoseps. 



bb. Costal grooves 13. Hemidadylimn, p. 32. 



aa. Posterior digits 5. 



b. Mandibular teeth small, numerous, terete. 



c. Premaxillaries not ankylosed ; costal grooves 10 to 19. 



Plethodon, p. 33. 



cc. Premaxillaries ankylosed ; costal grooves 17 ; color, pale 



yellow. Georgia. Stereochilus. 



bb. Mandibular teeth, few, small, knife-shaped. Pacific States. 



Autodax. 



*The three subfamilies of PlethodontidiB are founded on internal characters, and re- 

 quire some dissections. These, however, are not difBcult to make. By making a short in- 

 cision along the back of the specimen in hand, dressing away the museul.ir tissue down to 

 the vertebral column, and then sharply bending the back so that two of the vertebra sepa- 

 rate, it may be seen whether the anterior rounded head of the vertebraj is made of cartilage 

 or bone. If it is of cartilage, the vertebraj are amphica3lous; if of bone, opisthocoilous. In 

 either case, the posterior end of the vertebral centrum is concave. In like manner, the 

 wrist and ankle may be dissected and the determination made whether the nodules found in 

 them are composed wholly of cartilage or are bony. Since, however, we have no species of 

 Thoriina, this examination is not necessary. It may facilitate the determination to recollect 

 that the species of Desmogn 'thvs resemble in easily observed characters the species of 

 Plethodon only, and the descriptions of these should be carefully scanned. 



