324 GEOLOGICAL SURVEY OF THE TERRITORIES. 
paring every part of the 1st and 2d pairs of feet of individuals from 
Cape Saint Lucas and Kansas no differences can be found. 
As the species has proved to be the most abundant and accessible of 
all the species in this country, the specific name is not altogether ap- 
propriate, still it will serve to remind one of the interesting features in 
its geographical distribution. 
The food of this species appears to be Crustacea, as in dissecting the 
mouth-parts of one of this species the legs of an Asellus-like Crusta- 
cean were found partly swallowed. Hence they are quite predaceous in 
their habits. 
APUS LONGICAUDATUS Leconte. 
Plates XVI figs. 4, 4a; XVIII, figs. 4, 6; XIX, fig. 4; XX, figs. 3, 4. 
Apus longicaudatus Lec., Annals N. Y. Lyceum, iv, 155, Pl. IX, 1846. 
Apus obtusus James, Long’ s Expedition, ii, 336. Packard, Hayden’ 3 U.S. Geol. Survey, 
Terr. Report for. 1873, 620, 1874. 
Carapace about as long as wide, being shorter than in any other 
known American species. This species, besides the characters given by 
Leconte, has the following: The frontal doublure is about one-half as 
long in proportion as in vi cancriformis, being shorter than the hypo- 
stoma; the latter is rather shorter and broader than in A. caneriformis, 
and with a swollen area or eminence at the base, not present in A. can- 
criformis. The antenne are two-jointed, the 2d joint slenderer, more 
chitinous than in A. cancriformis, and reaching to within a distance 
from the edge of the shield equal fo one-fourth of theirlength. The 1st 
pair of feet are alike in both sexes. The endites are long and slender, 
differing only slightly from those of A. lucasanus; the specifie differ- 
ences are, however, best marked in the exites of all the limbs, the 
gills being small, rather narrow, but still wider than in A. lucasanus, 
but without the fringe of coarse filaments of the latter species; the fla- 
bellum is shorter, more triangular, the anterior edge being less full and 
rounded. In the 2d pair of feet the endites are much as in A. lucasanus, 
but the scale is long, knife-shaped, acute, and extends nearly to the tip 
of the 5th endite. ‘Lhe gill is regularly rounded, ovate, and the flabel- 
lum is subtriangular. 
In the 10th pair of limbs, while the endites are much as in A. luca- 
sanus they are a little narrower, and while the flabellum is of nearly the 
same shape and size, the gill itself is much shorter and broader, being 
nearly round. 
In the 11th pair of female limbs bearing the ovisacs, the short flabella 
are longer and narrower than in A. equalis. ° 
Seen from above, 32 segments may be counted in the males (in the 
female, 28) beyond the edge of the carapace; and seen from beneath, 
there are 14 segments beyond the last pair of appendages (in the 
female, 10). 
The abdomen is unusually spiny, as also the caudal stylets, the seg- 
ments of the latter being well marked by the spinules, which project 
unusually far out. The “telson is shorter and more spiny than in A. 
lucasanus ; on the upper side is a median group of three spines arranged 
in a triangle, with a pair lower down, with three stout lateral spines, 
and a group of five or six spines just within the outer edge, and near 
_ the base of the telson; the under side is more heavily spined laterally 
than in A. lucasanus, and there are more numerous, finer spines on the 
under side of the segment next in front of the telson. 
