184 DIPTEEA 



1. Atomosia ? 



Hab. Costa Rica, Cache {Rogers). 



This insect has the usual metallic greenish-black body ; the latter densely punc- 

 tate, the punctures being beset with minute golden hairs ; the abdominal segments 

 edged with white, less distinctly so on the basal segments. Legs black, beset with the 

 usual hairs and bristles ; the extreme base of the femora with a brownish-yellow ring, 

 which is narrow on the four anterior legs, much broader on the posterior pair ; knees 

 and the base of the tibiae also brownish-yellow ; hind tibiae, except the distal third, 

 yellowish-brown. Wings greyish, their basal third more hyaline. 



2. Atomosia nmcida, sp. n., <? $ . 



The black ground-colour hidden, especially on the thorax, by a dense, appressed pale golden pubescence ; pras- 

 scutellar callosities reddish-yellow ; legs pale yellowish, the fifth joint of the tarsi brown ; wings hyaline. 

 Length 8-9 millim. 



Hab. Mexico, Presidio (Forrer). 



Head pale yellowish-white pollinose ; mystax pale yellowish-white ; beard purer 

 white. Antennae: first joint rather long, reddish, the third linear, about one and a 

 quarter times the length of the first two together, brown, sometimes reddish at the 

 base. Thorax : dorsum densely clothed with an appressed pale golden-yellowish pubes- 

 cence, concealing the dark ground-colour ; pleurae grey-pollinose ; praescutellar callosities 

 reddish-yellow ; the bristles pale ; scutellar macrochaetae rather weak. Halteres yellow, 

 the knob sometimes lemon-yellow, sometimes reddish. Abdomen of the usual shape 

 and with the usual punctate sculpture, clothed with a dense pale golden-yellowish 

 appressed pubescence, the pubescence not quite so dense as on the thorax ; the silvery 

 hind edges of the segments visible in a certain light only — those on segments 4 and 5 

 more distinct than the others. Legs yellow or reddish-yellow ; last tarsal joint, except 

 its base, brown or black ; ungues black, red at the base. Wings subhyaline ; costa, and 

 the auxiliary and first veins, reddish-yellow, the other veins brown. — Five specimens. 



N.B. — The structure of the antennae agrees with the genus Cerotainia, but that of 

 the first two posterior cells is not like that described by Schiner. Is Cerotainia a good 

 genus 1 I have no specimen for comparison. 



The following species from Mexico (there are none from other parts of Central 

 America) described by earlier writers also belong to this genus : — 

 Atomosia beckeri, Jaennicke, Neue exot. Dipt. p. 51. 



C?) bigoti, Bellardi, Saggio &c. ii. p. 20. 



macquarti, Bellardi, 1. c. p. 20. 



sericans, Walker, Trans. Ent. Soc. Lond. n. ser. v. p. 282. 



soror, Bigot, Ann. Soc. Ent. Fr. 1878, p. 236. 



