174 NEW YORK STATE MUSEUM 



KEY TO SPECIES OF DIAMESA 



Larvae 



a Mouth parts as shown on pl.20, fig.9 1. w a 1 1 1 i i 



aa Mouth parts as shown on pl.36, figs. 18 to 25 ; the dorsal surface of the 

 abdominal segments marked with transverse fasciae (European 

 species) 3. culicoides 



Pupae 



a Anal end with six slender filaments 1. waltlii 



aa Anal end with eight filaments -.B. culicoides 



Imagines 

 a Halteres pale yellow ; thoracic stripes black ; length 4.5 to 5 mm. (United 



States, Europe, Greenland) 1. waltlii 



aa Halteres white ; thoracic stripes cinereous black ; length 2.75 to 4.25 mm. 



(Greenland) 2. chorea 



I cannot separate aberrata Lundbeck (1898) from 

 waltlii. 



1. Diamesa waltlii Meigen 

 1838 Diamesa Meigen. Syst. Beschr. 7 : 13, 1 

 1856 Ghironomus Halid. in Walk. Ins. Brit. Dipt. 3 : 194 

 1864 Diamesa Schiner. Fauna Austr. 2 : 615 

 1898 Diamesa aberrata Lundbeck. Vidensk. Meddel. 289, 77 



Larva. (Pl.20, fig.9) The larvae were taken in company with 

 the larvae of Thalassomyia fusca among the algae on 

 the surface of rocks over w-hich the water flows rapidly. In color 

 it is pale gr^en, in general appearance and even in many details 

 of structure it greatly resembles Thalassomyia fusca. 

 The dorsal selerite of the head is elongated, shield-shape, with 

 two pairs of marginal setae; on the lateral selerite the^'e is one 

 seta near the base of the mandible just above the lateral line, 

 one pair below this one and a little cephalad; another pair about 

 one quarter of the length of the head caudad of these but lying 

 as far below the lateral line as the first is above. Directly caudad 

 of the first, but midway between the front and hind margin of the 

 head, is another ; close to the dorsal suture, one quarter the length 

 of the head cephalad of the caudal margin is still another; and 

 finally there is a single one on each side at the base of the labium. 



The mouth ])arts are as shown in tlie figure. The epipharynx 

 is shown with its i)arts extended. In the figure given by the 

 writer in W\\\. CS. N. Y. State Museum (1903) these parts are 

 shown folded down. The lateral arms (la) are each expanded 

 apical]}" into a handlike process Avith 7 or 8 fingers. The mandi- 

 bles each have 5 blunt teeth, a fringe of coarse-branched hairs 

 projecting mesad. and two stout setae on the dorsal surface near 



