Dec, 1904,] Tabanidae. 219 



Chrysops Meigen. 



The species of this genus have fairly good characters. We 

 have recognized the males of a number of the western species, 

 but there are still several unknown. Twenty species are recog- 

 nized in the following pages, one described as new. I offer the 

 following key as an aid in separating them: 



1. Apex of the wing beyond the cross-band hyaline 2 

 Apex of the wing beyond the cross-band not entirely hyaline 4 



2. Abdomen yellow on the sides of at least the first two seg- 



nients excitans 



Abdomen uniformly black 3 



3. Base of the fifth posterior cell hyaline carbonarius 

 Base of the fifth posterior cell not hyaline mitis 



4. Second antennal segment decidedly longer than the third ceras 

 Second antennal segment not longer than the third 5 



5. First antennal segment distinctly enlarged 6 

 First antennal segment not enlarged 10 



6. First and second antennal segments distinctly enlarged virgulatus 

 Second antennal segment not distinctly enlarged 7 



7. Hyaline triangle separated from the posterior margin of the wing 



by an infiiscated space fulvaster 



Hyaline triangle reaches the posterior border of the wing 8 



8. Facial and frontal callosities almost entirely black or brown facialis 

 Facial and frontal callosities yellow or the latter margined with 



brown 9 



9. Slender species, male with base of anal cell hyaline, female with 



two small black spots on the middle of the second abdominal 

 segment _ pachycera 



Robust species, male with base of the anal cell infuscated, female 

 usually with a geminate black spot on the second abdominal 

 segment _ _ coquillettii 



10. A hyaline spot in the discal cell discalis 

 No hyaline spot in the, discal icell 11 



11. Whole face black in ground color 12 

 Part or whole of face yellow 14 



12. Abdomen yellow on the sides frigidus 

 Abdomen black 13 



13. Apical spot separated from the cross-band noctifer 

 Apical spot united with the cross-band nigripes 



14. Abdomen with longitudinal black stripes 15 

 Black abdominal markings not in the form of stripes 16 



15. Four black stripes rvmning the whole length of the abdomen sequax 

 Two black stripes running the whole length of the abdomen, the 



two lateral stripes abbreviated " pikei 



16- Frontal callosity yellow with narrow brown border coloradensis 



Frontal callosity black 17 



17. Cheeks entirely yellow furcatus 

 Cheeks with a black band from the eyes to the margin of the 



mouth " 18 



18. Yellow on each side of the second segrnent not enclosing any 



black, apex of the second basal cell hyaline for its entire 

 width ' lupus 



Yellow on each side of the second abdominal segment enclosing 

 a small black dot, hyaline at the apex of the second basal cell 

 crossed by brown 19 



