VARIATIONS OF GARTER-SNAKES. 5 



it is ascertained to what extent these characters are subject to modi- 

 fications? Only when this is known can we hope to accomphsh 

 much in our attempt to discover the origin of the present forms. 



This is very well illustrated in the synthetic taxonomic work that 

 has been attempted. Several efforts have been made to combine the 

 described forms into natural groups, and Stejneger, Brown, and A^an 

 Denburgh ° have, in various papers, endeavored to establish the 

 proper status of the different forms. The most comprehensive essay 

 is that of Brown (1901) in his "Review of the Genera and Species of 

 American Snakes North of Mexico," which appeared in 1901, and 

 which may be considered as a reaction from the extreme position taken 

 by Cope (1892) in his paper "A Critical Review of the Characters and 

 Variations of the Snakes of North America." In this work Brown 

 has attempted to unite the different forms into related groups, and, 

 as will be shown later, has succeeded very well in some instances. 

 But commendable as are his efforts, the methods employed, it seems 

 to n\e, are unfortunate. For example, sirtalis, leptocephalus (ordi- 

 noides), hutleri, parietalis, and picJceringi (concinnus) are united in one 

 group on the basis of similarity in the scutellation without regard as 

 to whether or not the characters included under this head are influ- 

 enced by definite variation, and until this is determined there may be 

 another explanation for similarity in scutellation than community of 

 origin, namely, parallel development. 



That there is convergence among the garter-snakes is illustrated 

 by the fact that so high an authority as Boulenger (1893, 418) gave 

 it as his opinion that the type of hrachystoma (hutleri) was a specimen 

 of leptocephalus (ordinoides) , incorrectly labeled as to locality. As 

 Cope subsequently showed, there is no doubt as to the correctness 

 of the locality, so that it is highly improbable that the two forms are 

 directly related, and yet the parallelism is so close that if unlabeled 

 as to locality it is often very difficult to distinguish between speci- 

 mens of the two forms. (See also p. 188.) It is essential, therefore, 

 to determine first of all along what lines the present combinations of 

 characters may have developed, in order that there may be no 

 confusion by parallelism. 



Another prime objection to the synthetic work that has been 

 attempted is that the geographic prohahilities have been so largely dis- 

 regarded. A knowledge of the extent of the variation in any form 

 affords little evidence of affinities if the geographic trends are ignored 



'^ Garman's arrangement (1883) is in many respects the most comprehensive, as he 

 considers the group in detail. There is, however, so little basis given for the grouping 

 which he has adopted, and so many manifest errors, that his synopsis must be consid- 

 ered rather as an effort to reduce the number of species than as a rational attempt to 

 establish natural affinities. 



33553— Bull. 61—08 2 



