SOME NEW NEOTROPICAL SIMULIIDAE. 281 



Simulium placidum, sp. nov. 



Female. — Head black, gray pruinose. Frons moderately broad, narrowing 

 gradually but distinctly toward the antennae, with rather numerous, irregularly 

 disposed hairs, except on the disk. Antennae bluntly pointed, the first two joints 

 dull ferruginous, the others darker, finely hairy and pruinose. Scutum dull black, 

 very faintly gray pruinose on the disk, diffuse whitish pruinose toward anterior margin 

 and on the humeri, without distinct markings ; vestiture of pale golden hair-like 

 scales disposed in small, closely approximated groups which do not form regular 

 rows. Scutellum short and blunt, black, with transverse golden scales on the disk 

 and coarse black hairs along the posterior margin. Postnotum short, black. Pleurae 

 dull grayish black, slightly pruinose. Abdomen subcylindrical, black, the basal 

 segment strongly white pruinose, the three succeeding ones velvet-black, the last 

 four shining. Legs black, marked with white as follows : Anterior tibiae with the 

 basal half marked with white on outer side ; middle legs with the tibiae whitish 

 at base and the first tarsal joint white on basal half ; hind legs with the tibiae white 

 at base, the first tarsal joint white on basal half and with the extreme base black, 

 the second joint narrowly white at base. The abundant appressed hairs of the 

 femora and tibiae show a brassy lustre ; front tarsi compressed . Claws with a small 

 sharp tooth in addition to the basal callosity. Wings hyaline, the venation normal ; 

 thick veins dull brown ; anal field with the iridescence moderate and widely diffused, 

 predominatingly green and red. 



Length : Body about 3 mm. ; wing 3 '5 mm. 



Trinidad: Arima River, 3Lxii.l913; females taken in the act of ovipositing 

 (F. W, Urich). 



In most specimens the anterior coxae, trochanters and femora have a brown cast. 

 This species is closely related to S. orbitale, Lutz, and S. seriatum, Knab, and show.>< 

 the same character and disposition of the scales on the mesonotum. As in the latter 

 species, the frons narrows anteriorly and is devoid of scales, but it differs from it in 

 the coloration of the legs and in other details. S. giiianense, Wise, probably also 

 belongs in this neighbourhood, but the description is insufficient and I have seen no 

 specimens. In supplementary material, sent in alcohol, a male was found which 

 apparently belongs to the present species. It may be described as follows : — 



Male. — Holoptic, the eyes with coarse scattered hairs toward median suture, the 

 facets coarse above, very fine below antennae. Antennae black, much more slender 

 than in the female. Mesonotum short and very convex, before scutellum doubly 

 excavate and strongly declivous, velvet-black, the lateral margins and margin of 

 posterior ridge grayish black with leaden lustre, the posterior declivity leaden gray 

 and with a pair of large velvet-black spots. Scutellum very small, tubercular. Pleurae 

 grayish black, faintly pruinose. Front and middle pairs of legs longer and more 

 slender than in the female ; hind, legs shorter and more hairy, the tibia and first 

 tarsal joint more strongly incrassate, the latter with basal third only whitish. 



This species apparently does not attack man. Mr. Urich has kindly sent me the 

 following notes on the biology of this species :— 



Oviposition : The females hover over the stream where the current is strongest 

 and rushing over boulders forms miniature rapids. The object of this hovering is 



