INTRODUCTION TO THIRD EDITION 



THE second edition of the Check List, which appeared in 

 1923, is now out of print, and the great volume of addi- 

 tions to our knowledge of American reptiles and amphibians 

 has been used in preparing this third edition. 



Many colleagues have aided us with helpful criticism and 

 suggestions. It is impossible to mention the names of all with 

 whom we have corresponded, but some have been of such 

 great and constant assistance that they should be especially 

 remembered. Our hearty thanks are particularly due to 

 Mrs. H. T. Gaige, Professor E. R. Dunn, Mr. L. M.Klauber, 

 Mr. K. P. Schmidt, and Dr. Frank N. Blanchard, and also 

 to Messrs. C. L. Walker, O. C. Van Hyning, and G. M. 

 Netting. 



It may perhaps be well to restate here the spirit by which 

 we have been guided in preparing this list. In general we 

 have been inclined to admit all forms described since the last 

 list unless they have been shown publicly to be untenable or 

 unless we have a decisive opinion of our own or some other 

 sufficient reason for rejecting them. Doubtful names may be 

 included in the Check List for debate or as an index to litera- 

 ture. In the use of binominals and trinominals we feel in- 

 clined to exercise our own discretion. We are opposed to 

 mixing the biological idea of a subspecies with the conveni- 

 ence or inconvenience of a trinominal designation. We hold 

 a subspecies to be a form which is manifestly descended from 

 another form. If they are still forms connected by inter- 

 grades we accept trinominals unless the percentage of inter- 

 grades is so large that it becomes unprofitable so to do. But 

 if there is reason to believe that the connection between two 

 forms has once been broken and that the intergrades now 

 recorded are either the result of hybridization or individual 

 reversion, we see no gain in treating them trinominally, par- 



