325 



HABITS OF I^ARVAE 



The larvae are aquatic, occurring along with and having the same 

 habits as those of Stratiomyia and Odontomyia. 



HABITS OF IMAGINES 



The flies are rarely taken except by sweeping amongst vegetation 

 on the margins of streams or ponds, or on marshy ground. I have 

 not found them on flowers. One species I have taken in ntmibers on 

 the leaves of bracken (Pteris) in Europe. 



As there is no synopsis of the species of this genus for North 

 America the following key and revision is presented as an aid to 

 students. 



Key to Species 



imagines 



1. Thorax with 2 yellow lines on dorsum in addition to the pair on 



upper margins of pleurae 2 



— Thorax with 4 yellow lines on dorsum in addition to the pair on 



upper margins of pleurae 3 



2. Femora in part black centralis (p. 326) . 



— Femora entirely yellow approximafa (p. 326). 



3. Abdomen with a complete yellow fascia on third segment in addi- 



tion to the usual lateral spots variegata (p. 327). 



Abdomen with at most 3 spots on third segment, one in center and 



one on each side ** 



4. Central spot absent from third abdominal segment ; legs with black 



markings ; large species, 8 mm crotcJii (p. 328) . 



Central spot present on third abdominal segment ; legs, with the ex- 

 ception of the coxae, yellow; smaller species, about 5 mm 5 



5. Fourth abdominal segment with 2 small spots on center, the lateral 



pale marks very distinctly curved forward and widely separated ; 

 veins surrounding discal cell of wing distinct. .aldricM (p. 329), 



— Fourth abdominal segment without spots except the laterals ; veins 



enclosing discal cell indistinct -6 



6. The pale markings whitish ; lateral stripes on frons very slightly in- 



curved at upper extremity, not connected there (female) 



alhovittata (p. 330) . 



The pale markings sulphur- or lemon-yellow; lateral stripes on 



frons distinctly incurved and connected with each other at their 

 upper extremities (female) P^cta (p. 331). 



