ON THE BRITISH SPECIES OF SIMULIUM — II. 233 



more or less surrounding them.) Antennae and mentum as in S. morsitans, the 

 mentum however with a broader black terminal portion. Anal sucker and gills as 

 in S. morsitans. Skin round anus with some very minute scales, inconspicuous 

 even under a magnification of 300. 



Pupa. — Respiratory filaments about as long as the pupa, six in number, arranged 

 in three distinctly stalked pairs, the stalk of the uppermost pair nearly vertical, 

 slightly longer and thinner than that of the middle pair. All the filaments in the 

 vertical plane at the base, slightly and evenly tapering towards the tips, bases not 

 at all swollen. Cocoon as in S. ornatum. 



Habitat. — Weedy rivers of moderate current. 



Breeding Season. — -The jS.rst brood appears at the end of April ; we have yet no 

 clear evidence as to whether there is a second. A very few adults have been captured 

 in August, and Miss F. Collins collected eggs in May 1911 at a spot where S. venustum 

 was abundant, but these may have belonged to some other species. 



Material collected. — ^Larvae and pupae : New Forest, Hants., 1-3. v. 1920 ; numerous 

 on grass and Ranunculus in Lymingfcon River at Brockenhurst Bridge, also a few 

 specimens in small streams running into Beaulieu River. Pupae : West Moors, 

 Dorset, v. 1911 {Miss F. Collins) ; R. Granta near Cambridge, 28.iv.16, on Ranunculus 

 with S. equinum ; Stapleford, Cambs., 28.iv.16, one on grass at edge of stream, with 

 S. ornatum. Adults, additional localities : Horley, Surrey, v. 15 (G. A. H. Bedford) ; 

 Oxford district, v. 16 {A. H. Hamm) ; Letchworth district, v. 17, v. 18, v. 19, often 

 at considerable distances from the nearest possible breeding places, some males as 

 far as two miles ; New Forest, 1-3. v. 20, numerous in various localities, males 

 swarming, females entering tent ; Shrewsbury, 21.vii.20, one female. 



References. — The pupa described and figured by Otto Fabricius (Schriften der 

 Berl. Ges. Nat. Freunde, v, 1784, pp. 254-259, pi. iv) as that of S. sericea, Linn., 

 may possibly be this species. Fabricius found the pupae in July on Potamogeton 

 lucens in Norwegian rivers. 



A pupa figured (though not named) by Vogler (Mitt. Schweiz. Ent. Ges. vii, p. 279, 

 1886) is almost certainly S. austeni. Vogler found it in company with S. equinum 

 (which he also figures) on Ceratophyllum and other water-plants in the river Rhine. 



S. austeni is so extremely closely allied in all stages to the North American 

 S. venustum, Say, as figured by Malloch and Pomeroy, that it cannot be ranked as 

 more than a local race. I have compared the genitalia of British specimens with 

 those of a specimen from Spartanburg, S.C. (A. W. Pomeroy) and can find scarcely 

 any difference. Both males and females are otherwise indistingaishable, and there 

 is no structural difference in the larvae or pupae. Even the head markings of the 

 larva are of the same type, though most of the British specimens examined had the 

 dark markings developed to a somewhat less extent ; examples could probably be 

 found however to match Pomeroy' s figure exactly. Though structurally identical, 

 the two races seem to have developed biological differences. Pomeroy states that in 

 America S. venustum female is abundant from early spring to late autumn in the 

 ears of horses, and that there are three or four broods in the year. In this country, 

 as mentioned above, there seems to be normally only a single brood, while no examples 

 have so far been found in horses' ears. 



