ON THE VARIATION OF THE PIT-VIPER. 163 



8. On the Variation of the Pit- Viper, Lacliesis atrox. 

 By Miss Joan B. Procter, F.Z.S. 



[Received March 19, 1918 : Read April 9, 1918.] 



(Text-figures 1-5.) 



Index. 



Page 

 Variation and ^Etiology (Evolution, heredity, etc.). Variation 



in Lacliesis atrox; derivation of markings 167-180 



Systematic (New names or changed names, or Varieties of 

 Xi. atrox ; revisions, discussions, or elucidations affecting 

 any part of the system, to be indexed under the names)... 163-167, 180 



The distinction of the forms, whether they he regarded as 

 species or as varieties, which cluster around the tropical American 

 Pit-'Viper, Lachesis atrox L., and of which the principal are 

 L. lanceolatus Lacep^de, L. jararaca Wied, and L. jararacussu 

 . Lacerda, is a subject which needs renewed investigation, especially 

 in view of Dr. Vital Brazil's recent publications*, in which he 

 claims specific rank not only for X. lanceolatus but also for 

 L. jararacussu, which has generally been regarded as a mere 

 colour variety. 



Mr, G. A. Boulenger, who has kindly helped me with advice in 

 my study of reptiles, suggested to me that I should take up this 

 investigation, and he has given me not only access to the collection 

 in the British Museum, of which he is in charge, but the benefit 

 of his experience, especially as regards the bibliography of the 

 subject. My best thanks are due to him for these favours, 



I. Historical. 



The nvxmber of names which Mr. Boulenger has quoted under 

 the synonymies of L. atrox and L. lanceolatus is very great, but 

 for my present purpose it will be sufficient to discuss only the 

 principal, such as have had more general currency, or which are 

 accompanied by figures enabling me to form an opinion on the 

 forms for which they ai-e intended. 



The earliest name is that of Coluber atrox Linnfeus, Mus. Ad. 

 Frid. (1 754) pi. xii. fig. 2. The specimens are described as having — 

 ventrals 200 and 196, subcaudals 70 and 67 pairs, and scales with 

 '■•carina elevata." However, Mr. L. G. Andersson, Oat. Lin. type- 

 spec. Sn. (Bih. Sv. Vet.-Ak, Handl. xxiv. iv. No. 6) p. 19, has 

 been abFe to supplement this definition, as he has had access to 

 the type-specimens in the Stockholm Museum, and he finds that 

 the keels on the scales " are low and extend nearly to the tip 

 of the scales," thus agreeing with Mr. Boulenger's L. lanceolatus, 



* La Defense coutre I'Ophidisme. Sao Paulo, 1911, 8vo. 2nd edition, 1914. 



11* 



