448 THE AMERICAN NATURALIST. [Vou. XXXII. 
sides of the cord. While a group near the middle of the animal may 
contain as many as twenty-five eyes, near the anterior or posterior 
ends a group may be represented by a single eye only. Eac 
eye is composed of a sensory cell, so surrounded by a pigment 
cell that the former is accessible to light only from one direction. In 
general, the eyes ventral to the central canal face ventrally, as do 
those in the right half of the cord, while those in the left half face 
dorsally. Notwithstanding these anatomical differences, the living 
animal shows no special response to light coming in a particular 
direction. CHP 
Note on the Mydaidæ of New Mexico. — Prof. S. W. Williston has 
recently published (Zy. Kansas Acad. Sci., vol. xv) some interesting 
notes on these curious flies. He remarks: “ Collections of Diptera, 
even large ones, rarely include many specimens or species of Mydai- 
dæ.” They are, in general, of southern distribution, though one 
species (Mydas clavatus) occurs rarely in Massachusetts. The first 
species observed in our region were those taken by Captain Pope on 
the Pecos River, somewhere about the Texas and New Mexico 
boundary. No less than four species: from Pope’s collection were 
described by Loew, as Zeptomydas venosus, Mydas luteipennis, M. sim- 
plex, and M. xanthopterus. Dr. Williston, in his paper cited, adds a 
new species, Zctyphus townsendi, collected by Townsend at Las Cruces, 
N. M.; and also records Mydas decar O. S., and M. basalis Westw., 
as taken in New Mexico by F. H. Snow, but unfortunately omits to 
say just where. 
On June 27, 1897, the writer was collecting grasshoppers with Mr. 
A. P. Morse, of Wellesley College, in the mesquite zone back of the 
Agricultural College, in the Mesilla Valley. Nearly at the same time, 
I took an example of Mydas carbonifer O. S., and Mr. Morse took 
one of M. luteipennis Loew, these being the first Mydaidæ I had come 
across in several years’ collecting. They were determined for me by 
Mr. Coquillett, of the Department of Agriculture. M. carbonifer is a 
black fly, well deserving its name, which seems to have a remarkable 
range. Osten Sacken’s type was taken by Professor Comstock at 
Norton’s Landing, Cayuga Lake, N. Y., and not only does it range 
south to New Mexico, but Williston (%c. cit.) refers provisionally to 
this species an example from Chapada, Brazil, doubtless collected by 
H. H. Smith, though it is not so stated. 
M. luteipennis, which was also taken by Pope, is a large blue-black 
fly with red wings, so closely resembling Pepsis rubra, a formidable 
