106 R. W. CROSSKEY 



inal pattern and pollinosity forms a useful distinguishing feature for the subgenus 

 (in addition to those mentioned below). 



The male hypopygium in Tetisimtdium is of the same type as that in Odagmia and 

 Simulium s. str., having a generally similar form of ventral plate to that found in 

 Odagmia (although lacking such a definite beak-like process as in this subgenus) , and 

 having similar long heavy styles, similar median sclerite and the same form of para- 

 mere and parameral hooks, and there seems no doubt that Tetisimulium is closely 

 related to both Odagmia and Simulium s. str. The pupal characters are essentially 

 the same as in these subgenera, and the fenestrate cocoon is like that of many forms 

 of Simulium s. str. (including Gnus), although it may be noted that Tetisimulium 

 pupae normally only have a dorsal spine-comb on the eighth abdominal tergum, 

 whereas pupae of these other subgenera most often have spine-combs on some 

 adjacent segments in addition. The larval stage in Tetisimulium is closely similar to 

 that of Simulium s. str., with bare cuticle, large pointed and broadly sagittate or 

 subcordate postgenal cleft, and with an indefinitely pigmented head in which it is 

 difficult to classify the pattern as being either positive or negative (though probably 

 a basic negative pattern since the areas of the spots are normally paler than other 

 parts of the head capsule). All three subgenera Tetisimulium, Odagmia and Simu- 

 lium s. str. agree in having the female cibarium minutely toothed between the 

 cornuae. 



Apart from the female pattern already discussed, Tetisimulium differs from 

 Odagmia and Simulium s. str. by having a very slender fore tarsus (Text-fig. 85) in 

 both sexes, and differs from Simulium s. str. (but not from Odagmia) in having the 

 pleural membrane haired. The larva has a much larger and more pointed postgenal 

 cleft than that of Odagmia larvae, and has no definite ventral papillae (small bluntly 

 rounded papillae are usually distinguishable in Odagmia) ; there appears to be no 

 satisfactory character separating larvae of Tetisimulium from those of Simulium 

 s. str. but the first mandibular comb-tooth seems usually to be much larger, and the 

 second and third comb-teeth relatively much smaller, in Tetisimulium larvae. 



The Nearctic subgenera Hagenomyia Shewell (see Introduction) and Psilozia 

 Enderlein (of which the latter occurs in Greenland and Iceland as well as North 

 America) have a strong resemblance to the Palaearctic Tetisimulium and may be 

 rather closely related to it, more especially Hagenomyia : the females of all three 

 subgenera are very similar because of the contrasting pale grey and blackish 

 patterned scutum and abdomen, and (like Tetisimulium) females of both Hagenomyia 

 and Psilozia differ from Simulium s. str. (including Gnus) and Odagmia by having 

 the large abdominal tergites 6-8 grey pollinose instead of shining blackish. The 

 scutal pattern in the females of Hagenomyia and Psilozia, however, includes a 

 blackish brown lyre-shaped mark in addition to the three broad brownish vittae 

 such as occur in Tetisimulium (these, though found in Hagenomyia and Psilozia, are 

 less conspicuous in these subgenera and it is the narrower blackish lines of the lyre- 

 shaped mark that stand out). Both Hagenomyia and Psilozia have the pleural 

 membrane bare and differ in this respect from Tetisimulium, and the ventral plate of 

 the males is of very different shape, but the three subgenera agree in having the fore 



