54 COSTA RICAN DIPTERA 



straight but oblique in profile, and most prominent at the epi- 

 stoma. The mesonotum is flattened and the scutellum large and 

 rounded in outline. The mesonotal setulae are arranged in well 

 separated rows. In other characters it is similar to Psilopa. 



Genotype. — Plagiops nitidifrons new species. 

 Plagiops nitidifrons new species PI. Ill, fig. 12. ' . 



Black; antennae, apices of tibiae, and all tarsi, pale. Halteres black. 

 Wings yellow, hyaline with bases as far as middle of costal cell and small cross 

 vein and basal third of anal cell blackened; apex of costal cell clear; veins 

 pale. Shining, with frons, face, and abdomen, highly polished and metallic 

 tinged. Mesonotum with transverse micro-rugose sculpturing; scutellum 

 convex, slightly sculptured, broader than long. Length. — 2.2 mm. 



Type. — cf ; Guacimo, Costa Rica, June 6, 1909, [Type No. 

 6127]. Paratypes. — 1 9 ?, topotypical. 



Two more specimens of this species were also collected : Over 

 mud at Peralta, August 7, and at Alajuela, September 15. 



ALLOTRICHOMA Becker 

 1896. Allotrichoma Becker, Bcrl. Ent. Zeit., .xli, 121. 



This genus is allied to Discocerina, but the face is subtubercu- 

 late, or rather prominent medianly in form of a subconical, but 

 not noticeably shining, tubercle. This character is not so prom- 

 inent in the known Costa Kican species, but is quite evident. In 

 some species this tubercle is lovy, causing the lower portion of the 

 face to become protruding, but there is always an evident reces- 

 sion of the epistoma. 



Only the following species is known to occur in Costa Rica. 



Allotrichoma abdominalis Williston PI. Ill, fig. 6. 



1896. Hecamede abdominalis Williston, Trans. Ent. Soc. London, 1896, 398. 



1897. Allotrichoma abdominalis Williston, Kans. Univ. Quart., vi, 4. 



A species distinguished by having the face carinated above the 

 tubercle, and the third and fourth abdominal segments con- 

 spicuously silvery-white, which, in well preserved specimens, are 

 in strong contrast with the opaque brown basal segments and 

 the mesonotum. Length. — 1.5 mm. 



Eight specimens collected at Cartago, February 19, and over 

 mud along the Rio de las Canas, near Santa Cruz, January 30. 



