322 GEOLOGICAL SURVEY OF THE TERRITORIES. 
the lateral spines are minute; along the middle line are five spines; 
the lateral group near the base are arranged more in a line than in A. 
longicaudatus, where they form a more irregular group. The under sur- 
face is nearly smooth compared with A. longicaudatus or A. lucasanus. 
The caudal appendages are two-thirds as long as the body, and gradu- 
ally taper towards the tips instead of being suddenly thicker at base, as 
in A. longicaudatus, and are much less spiny. In A. longicaudatus there 
are four or five large stout, broad teeth on one side, while in, the pres- 
ent species there are a number of minute spinules around the basal as 
well as the terminal segments. Number of abdominal segments beyond 
hind edge of carapace, 29; number of segments behind the last pair of 
appendages, 11. 
Total length of carapace, 25""; length along the middle, 193""; 
breadth, 21". 
Length of dorsal keel of carapace, 124™7; from front end of keel to 
front edge of head, 74™™. 
Length of abdomen behind the carapace, 25". 
Length of caudal appendages, 26™". 
This species differs from A. longicaudatus and A. lucasanus, to which 
it is nearly allied in form and in geographical range, in the longer eara- 
pace, and shorter abdomen with its longer telson. It need not be con- 
founded with A. equalis, in which the carapace is much larger and longer 
and the telson much shorter, while the latter species is restricted to the 
eastern border of the Rocky Mountain plateau and to Texas and Mexico. 
It differs chiefly from A. longicaudatus aud A. lucasanus in the shorter 
endites and much longer, smoother telson, and the smooth, almost 
hairy, instead of spiny caudal appendages, and in the entirely different 
arrangement of the spines on the telson. 
Locality.— Utah, J. S. Newberry, No. 1.” Two females, Mus. Chi- 
cago Acad. Sc. Ogden, Utah, collected by Mr. Henshaw, Wheeler’s 
Survey, one female. In this individual there is one less spine on the 
middle of the telson than in the two others, and there are only eight 
instead of nine segments between the telson and the last pair of append- 
ages. The carapace does not differ, nor do the appendages. 
APUS LUCASANUS Packard. 
Plates XVI, figs. 2, 2a, 2b; XVIII, figs. 3, 5; XIX, figs. 1, 5; XXI, figs. 7, 8, 10, 12, 13. 
Apus lucasanus Pack., Amer. Journ. Sc. Aug., 1871. Bull. U.8. Geol. and Geogr. 
Survey, iii, No. i, 171,179, April 9, 1877. 
Males.—This is the more aberrant of the two sexes. It is very near 
A. longicaudatus. The eyes and post-ocular tubercle as in A. longicau- 
datus ; the muscular eminence is not so much produced behind as in A. 
longicaudatus. Carapace a little longer than wide, with 14 teeth on 
each side of the posterior sinus. Doublure rather longer than in A. 
longicaudatus and the hypostoma a little smaller. Antenne as in A. 
longicaudatus. The 5th endite of Ist pair of feet are shorter than 
usual, often not reaching to the hind edge of the carapace, being much 
shorter than in any of the other American species. (It is represented 
as rather too long in fig. 2, Pl. XVI.) The first pair of feet and succeed- 
ing appendages are shorter and rather smaller than in A. longicaudatus. 
In the Ist pair of feet of male the 2d endite is much larger than in A. 
longicaudatus, the three other endites being much as in the male of 
A. longicaudatus ; the gill is narrow, regularly oval, and fringed with 
sparse, thick filaments, while the flabellum or accessory gill is full, 
