250 BUULETIN" 114, UNITED STATES NATIONAL MUSEUM. 



nated in some portion of the region between Texas and Nicaragua. 

 This, together with the fact that the only forms of doubtful relation- 

 ships are located in this region, indicates that the center of dispersal 

 of the entire genus is in the Southwest. 



Let us now consider how the genus as a whole answers to the criteria 

 for determination of centers of dispersal, as formulated by Adams 

 (1902, 122). There are 10 of these criteria, as follows: 



1. Location of greatest differentiation of a type. 



2. Location of dominance or great abundance of individuals. 



3. Location of synthetic or closely related forms (AUen). 



4. Location of maximum size of individuals (Kidgway-Allen). 



5. Location of greatest productiveness and its relative stability, 

 in crops (Hyde). 



6. Continuity and convergence of lines of dispersal. 



7. Location of least dependence upon a restricted habitat. 



8. Continuity and directness of individual variations or modifica- 

 tions radiating from the center of origin along the highways of 

 dispersal. 



9. Direction indicated by biogeographical affinities. 



10. Dii'ection indicated by the annual migration routes, in birds 

 (Palmen). 



Some of these criteria are of only limited value, and the fifth, 

 ninth, and tenth can not be used at all in the present instance. The 

 others wiU be discussed in order. 



1. Location of greatest differentiation of a type. — In the Southwest 

 we have polyzona, nelsoni, annulata, leonis, calligaster, splendida, 

 pyrrhomelaena, ruthveni, and alterna. The only region at aU com- 

 parable with this in diversity of type is the Southeast. Here we 

 have four forms, all specialized, and two of them {elapsoides and 

 rJiombomaculata) obvious derivatives of western types; but there is 

 no representative of pyrrhomelaena in the Southeast, nor of mexicana, 

 nor of alterna. The greatest differentiation is therefore imquestion- 

 ably in the Southwest. 



2 . Location of dominance or great abmndance of individuals. — ^This 

 criterion is of only minor value; exceptions may be readily called to 

 mind. It is valueless in this case, however, since, in the present 

 unsatisfactory state of our knowledge, there is as much to be said 

 on one side as on the other. 



3. Location of synthetic or closely related forms. — It has been noted 

 frequently that those forms of this genus to which the groups trace 

 their origin are more closely allied in structure with each other than 

 with any of the other forms in the genus. For example, the south- 

 western types, calligaster and leonis may, much more readily than 

 the specialized rhomhomaculata of the Southeast, be associated with 

 the GETTJLTJS group, and it is with the western representatives of 



