PROCEEDINGS OF THE UNITED STATES NATIONAL MUSEUM 



issued l^^tVA- sL^Mj) h 'Ae 



SMITHSONIAN INSTITUTION 

 U. S. NATIONAL MUSEUM 



Vol. 91 Washington : 1941 No. 3130 



NOTES ON THE SNAKE GENUS TRIMORPHODON 



By HoBART M. Smith 



There are 13 forms definable at present in the colubrid genus 

 Trimorphodon. These very readily fall into two groups of six or 

 seven forms each, one characterized by presence of large, V-shaped 

 marks on head and neck {hiscutatus group), the other characterized 

 by a transverse, light nuchal collar of varying width {upsilon group) . 

 The forms contained in the hiscutatus group are hiscutatus biscufatios, 

 h. quad7'uplex, paucinmculatus^ lyrophanes^ lambda^ and vanden- 

 hurghi. The members of the upsilon group are latifascia, fascio- 

 lata, upsilon^ collaris, tau^ vilkinsonii, and forhesi. These two groups 

 form natural assemblages that certainly are of subgeneric rank. 



In Trhnorphodon^ as in many other genera of snakes, evolution 

 has produced but few morphological innovations, and those that have 

 been produced are evident almost universally in terminal species that 

 appear to have been recently differentiated from a generalized stock. 

 Evolution in this genus has been evidenced chiefly in pattern ; this is 

 the basic medium of speciation. Accordingly, differences in species 

 are to be sought primarily in the pattern, only secondarily in mor- 

 phology. Likewise, relationships and direction of evolution must be 

 traced through pattern changes, not by morphological variations. 



Fortunately many of the steps in pattern evolution are shown or 

 indicated by species yet extant. The most important steps of all, 

 however — those that link the two radically different head and neck 

 patterns of the two groups — are lacking completely, and are not even 



408590—41 1 149 



