THE SNAKE GENUS TRIMORPHODON — SMITH 



151 



remain evident as very small blotches. In lambda the process of 

 suppression is complete; the secondary bands are scarcely evident. 



Obviously this succession of pattern types {paumTnaculatus to 

 'vandenhurghi to lyrophanes to lariibda) is not to be considered as an 

 indication of a similar succession in species evolution, for the 

 morphology here shows otherwise. Certainly lyrophanes and vanden- 

 hurghi have been isolated for a long period from pauelniaculatus, 

 since in them has been developed a spineless (i. e., very minute 



Figure 37. — Diagram of the possible phylogeny of Trimorphodon. 



spines) hemipenis. For some reason pattern change in vandenhurghi 

 ceased or greatly slowed, and perhaps through its influence lyro- 

 phanes did not reach the stage of complete suppression of alternate 

 blotches that characterizes lainbda. The latter, of course, did not have 

 the retarding influence of vandenhurghi j' and presumably its genetic 

 (and geographic) differentiation from pauchnaculatus was made 

 complete at an early date — very likely at the time the lyrophanes- 

 vandenburghi stock was isolated. 



