SNAKES OF THE GENUS PITUOPHIS 77 



Habits and habitat. — Apparently nothing has been recorded of the 

 habits of ruthveni. They are, however, probably similar to those of 

 the other subspecies of melanoleucus. 



Affinities. — This form is morphologically as well as geographically 

 intermediate between P. sayi sayi and the more eastern subspecies of 

 P. melanoleucus, since it is nearer than the other forms of melanoleucus 

 to sayi in the number of scale rows, the shape of the rostral plate, the 

 proportionate tail length, and the number of spots. That m. melano- 

 leucus, m. mugitus, and m. lodingi are all derived directly from ruthveni 

 is indicated by the coloration and scutellation of these forms. Thus, 

 melanoleucus is easily derivable from ruthveni by an intensification of 

 the color of the spots accompanied by a diminution of ground color, 

 by a fusion of the smaller anterior spots in pairs, by an increase in 

 rostral length and in proportionate tail length, and by a decrease in 

 the numbers of scale rows and ventrals ; mugitus may be derived from 

 ruthveni by a uniform diminution of color, accompanied by a fusion 

 of the smaller anterior spots in pairs and their blending with the 

 ground color, and by an increase in rostral length, in proportionate 

 tail length, and in the number of ventrals; and lodingi is derivable 

 from ruthveni by a strong intensification of color throughout, producing 

 a uniform black above and slate-gray below, by an increase in rostral 

 length and in proportionate tail length, and by a decrease in the 

 number of scale rows. 



The possibility of accepting lodingi as phylogenetically intermediate 

 between ruthveni and either mugitus or melanoleucus is precluded by 

 the decidedly aberrant coloration of lodingi, and by the fact that it 

 apparently has advanced farther than the other forms in question in 

 increase in the proportionate tail length, and decrease in the nunaber 

 of scale rows. Similarly, mugitus cannot be accepted as intermediate 

 between ruthveni and melanoleucus, because of its coloration and the 

 opposing tendencies in scale change evident in the two derived forms. 



The probable affinities of ruthveni with the neighboring forms may 

 be expressed by the following diagram: 



sayi -^ruthveni— >lodingi 



^mugitus 

 Table 7 lists the specimens of ruthveni that have been examined. 



