696 Bulletin American Museum of Natural History [Vol. XL VI 



The forms of the genus Chilomeniscus are in considerable confusion 

 and by no means well understood. Without sufficient material at hand 

 to clear up the points in question, I prefer to lean to the side of the exces- 

 sive analysis rather than synthesis. Van Denburgh and Slevin (1913, 

 p. 410) reduce the genus to two species, stramineus from the Cape 

 area of Lower California, and ductus ranging from southern Lower Cali- 

 fornia, southeastern California, western Arizona, and Sonora. This view 

 is maintained by them in their recent list of Lower Californian forms 

 (1921a, p. 52), with the subsequent addition of a new form, C. punctatis- 

 simus from Espiritu Santo Island. 



Cope's analysis of the genus (1900, p. 948), unfortunately some- 

 what confused in compilation, recognizes, in addition to the well-defined 

 stramineus, three crossbanded forms, C. ephippicus, C. fasciatus, and 

 C ductus. Of these ephippicus and fasciatus have the venter immaculate, 

 with crossbands confined to the back, while ductus is sharply set off by 

 having the body completely encircled by black bands. This may well 

 prove to be a variable character, not of specific value, but I know of no 

 evidence at present of intergradation or variation in this character. 

 The scale character employed by Cope to separate fasciatus and ephippi- 

 cus, however, has been shown by Van Denburgh and Slevin (1913, loc. 

 cit.) to be invalid, and I follow them in uniting these two forms, but not in 

 uniting ephippicus with ductus. Van Denburgh and Slevin make no 

 mention of the coloration. The evidence presented by Mocquard for the 

 union of fasciatus and ductus (1899, p. 318) does not seem to be sufficient 

 for a final decision on this point. 



Reference to the following key will make clear the characters which 

 distinguish the forms recognized in the present analysis. It is notable 

 that C. ductus and C. ephippicus have broadly overlapping ranges, C. 

 ephippicus occurring alone in southern Lower California, C. ductus alone 

 in Sonora, while northern Lower California and the Colorado Desert 

 area have both forms. 



Key to the Species of Chilomeniscus 



1. Rostral not in contact with the prefrontals; no dark crossbands, each scale with 



a dark spot C. stramineus. 



Rostral in contact with the prefrontals; dark crossbands or rings on the body . 2. 



2. Body completely encircled by dark rings C. ductus. 



Dark crossbands on the back, venter immaculate 3. 



3. Crossbands about 25 C. ephippicus. 



Crossbands about 39, with or without dark spots on the scales of the light rings. 



C. punctalissimus. 



