648 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



NOMADA LIBATA Cresson. 



Female. — Custer County, Colorado (Cockerell). This fine species 



looks exactly like N. vallesina Cockerell, except that it is larger 



and more robust. The following differences appear on minute com- 

 parison: 



Inner orbits almost parallel; third antennal joint longer; anterior coxse with a rudi- 

 mentary spine; scutellum slightly bigibbous; apical part of flagellum darkened; 

 cheeks entirely red; tegulse large N. libata. 



Inner orbits diverging above; third antennal joint shorter; scutellum strongly bigib- 

 bous; apical part of flagellum red like the rest; posterior part- of cheeks black; 

 tegulae ordinary iV. vallesina. 



NOMADA SEMISCITA Cockerell. 



A male from Denver, May 26, 1898, has a short broad supra- 

 clypeal mark in the manner of N. martinella and scita. The species 

 differs from these by the comparatively short and thick fourth 

 antennal joint (in martinella this joint is quite long and excavated 

 on the outer side), the fifth joint with a prominent thorn-like spine, 

 the second s. m. receiving the first r. n. at the middle (beyond in 

 martinella), the postscutellum entirely black, the two light marks 

 on the first abdominal segment each inclosing a ferruginous spot. 

 In the new specimen the apical plate of the abdomen is strongly 

 notched. This is perhaps the male of N. frieseana. 



NOMADA SCITA Cresson. 



Males are from Denver, Colorado, May 26, 1898; Colorado, 2076 

 (Baker collection), and Los Pinos, Colorado, at Erigeron May 22, 1899. 

 This is smaller than male N. martinella, but on comparing a series 

 the supposed differential characters seem evanescent and I am not 

 altogether satisfied that the two species are distinct. The female 

 of N. scita has not been described, but one was taken by Baker at 

 Los Pinos, Colorado, on Erigeron, May 22, 1899. It is smaller and 

 darker than .V. martinella, but otherwise similar. Comparison was 

 made with the usual Colorado martinella; but the true type of that 

 species from New Mexico was small, though clear bright red. 



NOMADA MARTINELLA Cockerell. 



The U. S. National Museum contains 7 females from Colorado 

 (Baker 2076 and 1332). In my original description ** for Sioux City 

 read Sioux County. 



NOMADA (MELANOMADA) HELENIELLA, new species. 



Female. — Length 5-5| mm. ; head and thorax black, abdomen clear 

 red; mandibles rather dark red; face broad, covered with appressed 

 pale hair; antennae dark, third joint reddish, shorther than fourth on 



a Proc. Acad. Nat. Sci. Phila., 1903, p. 590. 



