68 On new Bees from New Mexico, U.S.A. 
occasion of a meeting of the College Field Club, April 27, 
1894. 
This species might be confounded with the Sta. Fé H. semz- 
ceruleus; but that differs in being larger, especially in the 
thorax, in its more distinctly sculptured metathorax, its con- 
spicuous erect pale brownish hairs on postscutellum, its more 
strongly and closely punctured mesothorax, its somewhat 
differently shaped head, with a green face, and its dark 
antenne. 
Of other species, //. reticulatus and H. Hartii differ at once 
from semibrunneus by the reticulated mesothorax ; H. apop- 
kensis, a Florida species, is like semébrunneus in lacking this 
reticulation, but it has the mesothorax only moderately shiny 
and its head and thorax are greenish. 
(8) Halictus perdifficilis, sp. n. 
9. Length about 63 millim. Head dark blue-green ; 
mesothorax and scutellum brassy green; metathorax so dark 
blue as to be almost black. Abdomen piceous, apical margins 
of segments 2, 3, and 4 slightly testaceous. Pubescence of. 
head and thorax sparse, thin, with a slightly yellowish tinge. 
Head moderately small; face not very broad, the portion 
between ocelli and antenne strongly and closely punctured ; 
flagellum dark chocolate-brown, not at all yellowish. 
Mesothorax minutely roughened and strongly and rather 
closely punctured ; median groove very distinct. Scutellum 
strongly punctured ; postscutellum with long subochraceous 
hairs. Enclosure of metathorax rounded behind, not bounded 
by a distinct line, rather strongly subreticulately wrinkled. 
Sides of metathorax with numerous whitish hairs. 
Legs dark, ordinary. Wings hyaline ; nervures and stigma 
pale honey-yellow; subcostal nervure black. Third sub- 
marginal net narrowing one-half to marginal. 
Abdomen pruinose from short greyish-white pubescence, 
except dorsum of first and second segments, which are bare. 
First segment with very fine scattered punctures; second 
segment with much closer punctures. ‘lhe shape of the 
abdomen is rather longer and more cylindrical than is usual. 
Hab. Santa Fé, N.M., July 4, 1894 (Ckll. 1228). 
At first it seemed very difficult to clearly separate perdifi- 
cilis from its allies; but close scrutiny shows it to be distinct. 
From semibrunneus it is recognized by its larger size, 
dullish thorax, mesothorax not so sparsely punctured and 
strongly green, and pruinose abdomen, 
H. pruinosus has the abdomen broader than that of per- 
