Occasional Papers of the Museum of Zoology 3 



Dizonias tristis Walker. — The extreme variation in color of 

 the members of this genus has been considered by several 

 authors, but none of them have come to a conclusion as to 

 the limits of the species. 



In a collection of twenty specimens, twelve males and eight 

 females, from Louisiana, Texas, Georgia, Alabama, and Flor- 

 ida there is much variation and the characters given for sep- 

 aration of the four recognized North American species do 

 not appear to be altogether reliable. One could easily find 

 color characters for the separation of several types that might 

 be called species among this material, but on account of the 

 gradual variations in the series and the results of studies that 

 others have made, the better disposition of the problem pre- 

 sented seems to be to consider all these specimens as belonging 

 to a single species. 



There is general agreement in the series in that all males 

 are predominantly black and all females are predominantly 

 brown. The white bands or zones on the second and third 

 segments which suggest the generic name are extremely 

 variable, being distinctly apparent in some specimens and 

 entirely absent in others, with various gradations, although it 

 may be said that when specimens become old and greased, as 

 they often do, the white color producing the zones is of such 

 a nature that it often becomes nearly obsolete. Aside from 

 these white zones, five males have the abdomen all black and 

 seven have the abdomen part brown; of the latter, two have 

 the last three segments brown and one has the abdomen all 

 brown beyond the middle of the second segment, while the 

 remaining four intergrade. In all males the extreme tip of 

 the abdomen is white-haired ; in nine males the hypopygium is 

 black, in three it is brown. In total length the smallest male 

 is 15 mm., the largest male is 22 mm. 



