60 
TRANSACTIONS OF THE TEXAS ACADEMY OF SCIENCE. 
in great abundance along the road between Lunas Well and Whitewater, 
on branches of Atriplex canescens. It has been described by Professor 
Cockerell as var. rubidus. This variety is of a pronounced reddish color, 
while the normal form is always whitish. The latter was originally de- 
scribed by Cockerell from the State of Chihuahua, not far north of Chi- 
huahua City, but has since been found abundantly in southern New Mex- 
ico. It has never been found to vary from its whitish color. While the 
new variety rubidus differs apparently only in color, the many extensive 
patches of it that were observed showed no departure from its character- 
istic red color. 
MESILLA VALLEY OF THE RIO GRANDE.— This locality has 
been referred by Professor Cockerell, in his monograph of Perdita (Proc. 
Acad. Nat. Sci., Phil., 1896, p. 31), to what he calls the Middle Sonoran , 
which he defines merely as the “lower part of Upper Sonoran.” I do not 
deem it advisable to further split the Upper Sonoran , which has already 
been split off from the Lower Sonoran. It will be useful, certainly, to 
refer to the Mesilla Valley fauna by a distinctive name, at least in time 
when all its affinities are worked out in detail, but I believe it should 
be ranked as a fauna, not as a zone or province. As a fauna, considerable 
other territory in Chihuahua, Texas, and Coahuila will go with it, as 
well as the Pecos Valley of New Mexico, etc. 
Diptera. — The following diptera, recently determined by the writer 
from the Mesilla Valley, are of interest from a biogeographic stand- 
point. 
1. Paragus tibialis var. dimidiatus Lw. — Las Cruces, August 21. 
On flov r ers of Aphantostephus arizonicus Gray. Not before recorded 
from New Mexico. Also taken at the White Sands, as already stated. 
Recorded from Sonora, Durango, and Guerrero (Biol. C. A. Dipt.). 
2. Nausigaster unimaculata Towns. — Rincon, July 5 (Ckll.). On Chil- 
opsis linearis. This is the first record of this species in New Mexico. 
The specimen is not typical. 
3. Mdanostoma slegnum Say. — Las Cruces, March 26 (Ckll.). This 
w r as taken in the Sacramentos, at the White Sands, and was collected by 
Cockerel] at Santa Ee. It occurs in the Colorado Parks, and seems par- 
ticularly a Transition and Upper Sonoran species. Yet it ranges ap- 
parently into the lower Boreal in Colorado and the Northwest, and into 
the Lower Sonoran and Neotropical in Mexico, being recorded from as 
low down as Orizaba (Biol. C. A. Dipt.). 
4. Eupeodes volucris OS. — Las Cruces, also Pecos Valley at Roswell. 
March and April. This distinctly Upper Sonoran species is common at 
Las Cruces, on flowers of Sisymbrium- canescens. 
