FLIES OF GENUS RIVELLIA — NAMBA 47 



Foul- general color forms can be separated. However, these cate- 

 gories are by no means distinctly delimited and individuals do exist 

 which mny be considered as intergi*ades between categories. Further- 

 more, there is no correlation between the color forms and their 

 geographical distribution. The four color forms will be described 

 separately here. 



Yellow form: Postcranium and thorax wholly yellowish. Legs 

 yellow except for middle and hind tibiae which are sometimes brownish 

 toward tip. Abdominal tergites vary from almost wholly yellow to 

 almost wliolly black. 



Specimens examined: Georgia (699, 2d^cf): Billy's Island 

 (Okefenokee Swamp), Tifton; May 28-Aug. 11. Florida (399, 

 Icf ): Hillsborough Count}' (Little jMantee River, U. S. Highway 41), 

 Bradenton, Fort Myers; March 11-July 14. North Carolina 

 (299, Icf): Raleigh, Everetts; June U-Early August. New 

 Jersey (499, Icf): Westfield, Anglesea, Elizabeth, Clementon; 

 May 21-July 22. New York (19): Flushing; June 15. Illinois 

 (19): Cabin Boat (INHS); July 1. 



Yellow-brown form: Postcranium brown or dark brown. Mes- 

 onotum dark brown or black; pleura j^ellovAsh, sternopleuron some- 

 times brown. Legs yellowish except for middle and hind tibiae, 

 which are brownish, and all tarsi, which are blackened toward tips. 

 Abdominal tergites usually dark brown or black. 



Specimens examined: Virginia (Icf): Great Falls; June 12. 

 New York (8 9 9, 9cfcf): Babylon, Bronx, Maspeth, Riverhead, 

 Mosholu, East Aurora, Orient, Oakdale; June 6-Aug. 12. Michigan 

 (19): Nottaw^a; Aug. 26. 



Brown form: Postcranium, thorax, and abdominal tergites con- 

 colorous, dark brown or black. Legs yellowish except for middle and 

 hind tibiae which are brownish and all tarsi which are blackened 

 toward tips. 



Specimens examined: Georgia (19, Icf): Griffin; Aug. 12. 

 New York (5 9 9 , 2 d^ d') : Flushing, Babylon, East Aurora, Oakdale; 

 June 3-July 22. New Jersey (19): West Orange; Sept. Michigan 

 (19): Gratiot County; June 17. 



Black form: Postcranium, thorax, and abdominal tergites con- 

 colorous, dark brown or black. Front legs: Coxae wholly yellow or 

 with brown spot on outside at base; femora whoUy yellow or yellow 

 inside and black outside; tibiae blackish toward base, yellowish to- 

 ward tip; tarsi yellow toward base, blackened toward tip. Middle 

 and hind legs: Coxae, femora, and tibiae black; tarsi yellow toward 

 base, blackened toward tip. 



Specimens examined: Georgia (2 9 9, 9cfc^): Atlanta, Griffin, 

 Adel; May 21-Aug. 12. North Carolina (499, Icf): Raleigh, 



