374 NEW VOKK STATE MUSEUM 



KEY TO SPECIES OF DIAMESA 



La7-vae 



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



aa Mouth parts as shown on pl.3(>. figs. 18 to 25 ; the dorsal surface of the 

 abdominal sogincnts marked with transverse fasciae (European 

 species ) 3. c u 1 i c o i d e s 



I'lipae 



a Anal end with six slender filaments 1. w a 1 t 1 i i 



aa Anal end with eight filaments 3. c u 1 i c o i d e s 



Imagines 

 a Ilalteres pale j-ellow ; thoracic stripes black ; length 4.5 to 5 mm. (United 



States, Euroi>e, Greenland) 1. w a 1 1 1 i i 



(HI Ilalteres white; thoracic sti-ipes cinereous black ; length 2.75 to 4.25 mm. 



( Greenland ) 2. chorea 



I canuot separate aberrata Lundbeek (1898) from 

 w a 1 1 1 1 i . 



1. Diamesa waltlii ^leioen 

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

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

 1864 Diamesa Schiner. Fauna Austi-. 2 : 615 

 1898 Diamesa aberrata Lundbeek. Videusk. ]Meddel. 289, 77 



Larva. (Pl.20, lis;.!)) Tlie larvae were taken in company with 

 the larvae of T h a 1 a s s o m via f u s c a among the algae on 

 the surface of rocks over which the water floAvs rapidly. In color 

 it is pale green, in general ap]tearance and even in many details 

 of strnctnre it greatly resembles T h a 1 a s s o m y i a f n s c a . 

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

 two pairs of marginal setae; on the lateral selerite there is one 

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

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

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

 as far beloAv 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 <[uarter 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 sjiow n in the tigure. The epipharynx 

 is shown Avith its parts extended. In the figure given by the 

 writer in liul. OS. N. Y. State Museum (l!)0:i) these parts are 

 shown folded down. The lateral arms ila) are each expanded 

 apically into a handlike process with 7 or 8 tingei-s. The mandi- 

 bles each have .1 blunt teeth, a fringe of coarse-branched hairs 

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



