92 BULLETIN 114, UNITED STATES NATIONAL MUSEUM. 



4. The young of yumensis, with possible exceptions near the 

 northern and western limits of its range, are like the adult, and if 

 there had never been a loylii-stsigQ between this form and conjunda, 

 the young of this latter would also be like the adult. But young 

 examples of conjunda are Hke hoylii in the character of the white 

 rings, their scales only with age attaining the basal shading, while 

 in head pattern and in shape of frontal they are like a variation of 

 hoylii that is not uncommon in some coastal portions of its range, 

 but not like any variations of yumensis. 



The basal shading of the white scales of conjunda, and the same 

 condition as an individual or possibly local variation in hoylii, is there- 

 fore to be regarded as a case of reversion to an ancestral type — analo- 

 gous to the development of white centers or bases on the dark scales 

 oifloridana. 



5. If, as noted elsewhere, nitida attained the Cape Region from 

 southwestern Califoniia, there is then no reason why conjunda may 

 not have done so, too. 



From the above considerations the following hypothesis is therefore 

 presented to explain the derivation of conjunda. Yumensis retained 

 its identity in the desert region of southern Arizona and the head of 

 the GuK of California, but northward, westward, and perhaps south- 

 westward, it developed into hoylii. The latter migrated south into 

 the desert of Lower California west of the mountains, and became 

 altered, somewhere in the peninsula, into conjunda, partially by the 

 development of new characteristics, or the accentuation ot certain 

 variations, partially by reversion to the pattern of its desert ancestor, 

 yumensis. 



