VI INTRODUCTION 



ticularly in those cases where each form may, in its own turn, 

 normally intergrade with other trinominals. We feel in- 

 clined to conserve the status of the names of the old list 

 except when absolutely compelled by the facts to make a 

 change. 



In some respects we may seem over-inclined to be thus 

 conservative. Dr. Dunn has recently proposed that the 

 genus Tropidoclonion be merged with Thamnophis. But 

 since the monotypic form is obviously more different from 

 any species of Thamnophis than any of the species in that 

 genus are one from another we prefer still to recognize the 

 peculiar genus for this single species. Considering, as we do, 

 that genera are groups for convenience, that no two people 

 are ever likely to agree for long on generic limitations, we feel 

 that any means of breaking up large genera by setting off 

 particularly well differentiated species or groups of species is 

 justifiable and praiseworthy. The recent attempt of Myers 

 (Proc. Biol. Soc. Wash., Vol. 43, March 12, 1930, p. 61) to set 

 up the name Bufo canagicus (Pallas) for Bufo boreas has not 

 seemed to us in the least convincing, and we are entirely in 

 agreement to ignore this name since it is impossible from 

 Pallas' description to know whether he had a Bufo or a Rana 

 in hand.^ 



Our hearty thanks are due to Mr. and Mrs. R. E. Bo wen 

 and Miss H. M. Robinson for their care in verifying refer- 

 ences and assisting in the preparation of the manuscript. 



T. B. 



1 It appears at the last minute, after printing of the text has been completed, that two 

 names have been inadvertently omitted: 



Elaphe lindheimeri Stejneger and Barbour (Check List No. Amer. Amph. Rept., 2nd Ed., 

 1923, p. 92) should appear as a synonym of Elaphe obsoleta confinis, p. 99. 



Chilomeniscus ephippicus Stejneger and Barbour (Check List No. Amer. Amph. Rept., 2nd 

 Ed., 1923, p. 102) should appear as a synonym of Chilomeniscus ductus, p. 114. 



