MAY FI.1KS AM) MIIMJKS OK \K\V VdltK 



j> 1 a I v p u s from Arizona and which probably also belongs to 

 this genus, making four species Ilius far known. 



The eggs of T. congrega I a are laid in strings of gelatine, 

 in which the elongate oval eggs are placed. The larvae of the 

 two species of which they are known live in rapidly flowing 

 \\aier. Here the larva spins upon the surface of ihe rock a 

 cocoon so loose, transparent, and open that it is not hidden by 

 it, though it prevents the larva from being washed away. The 

 larva greatly resembles Dii a m e s a from which the one Ameri- 

 can species which is known in the larval state can be distin- 

 guished by the form of its labium. The larva is pale green in 

 color with a dark brown head, and without blood-gills on the 

 ventral surface of the eleventh segment. The pupa is apparently 

 without thoracic respiratory organs; and the dorsal surface of 

 the abdomen is provided wilh numerous setae. 



Imago. The genus resembles in many respects both Ortho- 

 c 1 a. dins and I) i a in e s a ; from the former it may be distin- 

 guished by its having the fourth tarsal joint of all the feet in both 

 sexes obcordate and shorter than the fifth; from the latter genus 

 in having no M-Cu. crossvein I pi. .'SO, fig.ll'). 



Head" small, broad, eyes elongate, somewhat emarginate, ocelli 

 wanting. Antennae 14-jointed in the male, long, densely haired, 

 the 14th joint like that of h i r o n o m u s; antennae of female 

 7-jointed, sparsely short-haired, joints rounded, basal joint of 

 both male and female flattened, disk like. Palpi 4-jointed. 

 Thorax arched. Abdomen of the male moderately slender, of the 

 female shorter and stouter. Legs moderately slender, fore meta- 

 tarsus shorter than the tibia, the fourth tarsal joint of all the 

 feet in 'both sexes shorter than the fifth and obcordate. Wings 

 bare, venation resembling that of ()rt hocla d i us, the M-Cn. 

 crossvein wanting. The forking of the cubit us may be either 

 proximad or distad of Hie KM crossvein. 



KEY TO SPECIES OF THALASSOMYIA 



Imagines 



a Dorsum of thorax blackish with indications of three stripes; humoral 

 spots, scutellum, and pleura yellnwish or hruwnish : abdomen dull 

 black, first two segments greenish : li-ni. r ili 3 to 5 mm. (Now York) 



1. o b s c u r a 



aa Thorax black, humeral spot yellow; length 2.5mm. (Flagstaff, Arizona) 



2. platypus 



