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The vertebral ridge is more accentuated in the southern form, 

 although dissections of the neural spines of the anterior vertebrae 

 show no noticeable differences. The keels of the median scale rows 

 anteriorly are markedly different, however, as those of mexicanus 

 terminate in an enlarged knob near the posterior tip of the scale, 

 while those of nummifer reach the extreme tip ; in the latter the knob 

 is present but less distinct. 



A large nummifer (female) measures 573 mm. in total length; some- 

 what shorter than this are other females with well-developed young. 

 The larger male nummifer measures 567 mm. Apparently this species 

 is notably smaller than mexicanus, one specimen (female) of which has 

 been seen that measures 934 mm. in total length. The southern species 

 probably reaches a maximum length of about 1,100 mm. 



The southern form is distinctly shorter in proportion to body 

 diameter, and the head is somewhat larger; these have long been 

 known as characteristic features of the "jumping viper" (mexicanus). 

 In nummifer, however, the head and body are of more nearly normal 

 proportions. The differences are not of a type that may well be 

 treated statistically. 



It appears obvious that these two forms are distinct from each other 

 yet closely related. Whether they are separate species or are subspecies 

 is not clearly evident from data now available; certainly they are 

 members of a single morphologic group and have complementary 

 ranges, but this does not necessarily mean that an intergradation takes 

 place. Since all specimens can readily be differentiated, and there 

 is no overlap of variation in certain features differentiating them, it 

 seems best to consider the two forms as distinct species. 



Table 1. — Variation in Bothrops mexicanus 



BOTHROPS NASUTUS Bocourt 



Trim* resutyus nasutus Smith, Zoologica, vol. 2G, p. 62, 1941. 



One specimen was secured at Piedras Negras, Guatemala (No. 

 110415). It was found sunning itself among the loose rocks of the 



