2 BULLETIN 194, UNITED STATES NATIONAL MUSEUM 



differentiated species are shown to interbreed freely while other popu- 

 lations inadequately differentiated taxonomically are sho^^'ll to be in- 

 capable of interbreeding. Furthermore, determination of the actual 

 status of some forms which we here regard as species must undoubtedly 

 await experhnental investigation; we refer to extraordinary complexes 

 like that of a certain group of closely related but morphologically very 

 distinct species of Eleutherodactylus in central Veracruz (vide Taylor 

 and Smith, Proc. U. S. Nat. Mus., vol. 95, 1945, p. 572). Beyond 

 question, en fin, much juggling of arrangement remains to be endured. 

 This fact is a reflection of (1) the peculiar character of amphibians, 

 which are provided with fewer well-defined obvious and interracially 

 variable features than almost any other group of vertebrates, and 

 (2) the difficulties attending their collection. The difficulties of am- 

 phibian taxonomy are obvious to anyone who actually tries to identify 

 preserved specimens without the benefit of field experience. Knowl- 

 edge of the animals in life is practically indispensable even — or per- 

 haps especially — to the expert. Tbis fact has not always been appre- 

 ciated by critics who may have felt that we have recognized, in some 

 cases, more forms than exist. 



That thorough collection of amphibians is not easily attained, 

 especially in tropical areas, is weU known. Some specimens emerge 

 from their quarters into the open for breeding, where they are more 

 easily collected, for extremely brief periods' — perhaps one night a year. 

 Except in breeding congresses many species are rarely if ever found; 

 thus one must be on hand at just the right time and at just the right 

 place to secure the species. Salamanders are collected in abundance 

 usually by special techniques not widely apphed, such as seining or 

 use of dipnets (for ambystomids) and search during the dry season 

 in bromelias, stump holes, etc. (for most plethodontids). We have 

 continually been surprised by repeated discovery of novelties at 

 favorite collecting sites that we had considered completely surveyed. 

 In view of these considerations, we feel that our view of the relative 

 incompleteness of our present knowledge and the considerable length 

 of time that will be required to approach completeness is not unwar- 

 ranted. 



Nevertheless we feel the time is ripe for a summar}'^ of the amphibian 

 fauna of Mexico, the complexity of which has become steadily more 

 apparent in recent years. Students in this field have accomplished 

 reviewal of most available collections at least only in a preliminary 

 fashion, partly because of d\vindling accessions during war years. 

 The coming years will undoubtedly be a period of review, during which 

 the activities of the recent past and the problems revealed by them 



