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STEJNEGER : BATRACHIANS AND REPTILES. 223 



of small salt lakes," though they probably occupy somewhat different 

 stations. That two so nearly allied species should live together in so 

 close neighborhood without occasionally producing hybrids would be 

 highly improbable. The wonder is really that they are as pure bred as 

 they appear to be, and one would like to know the nature of the "isola- 

 tion " or " segregation " which accomplishes this result. That interbreed- 

 ing takes place occasionally, however, seems indicated by a specimen 

 brought home by Mr. Hatcher, which in many respects shows evidence of 

 being intermediate between the otherwise typical specimens of both species. 



This specimen (from jar lo) has somewhat smaller head scales than D. 

 bibronii, but larger than extreme D. davwinii, though there is a well-de- 

 veloped shield between first lower labial and first chin-shield behind the 

 mental as in the latter species. The coloration is also intermediate inas- 

 much as the cinnamon or rather vinaceous ground color of D. darwinii is 

 absent, while its broad semilunar white spots behind each dorsal black bar 

 on each side of the back are exactly as in the latter. The dense sprink- 

 ling of the upper ground color with dusky and the broad, distinct black- 

 ish cross bands on arms and legs are again indicative of D. bibronii, 

 while the absence of the characteristic fish-hook mark on the nape of the 

 latter is absent and replaced by the equally characteristic pair of spots of 

 D. darwinii. The black cross-bars on the back are located slightly differ- 

 ently in the two species, but their number is apparently the same. Here, 

 however, is a somewhat surprising deviation from both in the supposed 

 hybrid, inasmuch as it has one regular cross-bar more than either. 



This last feature might lead to the suspicion that we have before us the 

 possible representative of a third form. It is then very unfortunate that 

 the exact locality of each specimen is unknown. Under these circum- 

 stances there is nothing else to be done than to call attention to the facts 

 as represented above and to leave the clearing up of this, with so many 

 other questions, to the future explorers of Patagonia. 



