324 GEOLOGICAL SURVEY OF THE TERRITORIES. 



paring every part of the 1st and 2d pairs of feet of individuals from 

 Oape 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 ax)pears 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 Lee, Annals N. Y. Lyceum, iv, 155, PI. IX, 1846. 

 Apus obhtsus James, Long's Expedition, ii, 336. Packard, Hayden's U. S. Geol. Survey, 

 Terr. Report for"l873, 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 folloAying: The frontal doublure is about one-half as 

 long in proportion as in A. cancriformis, being shorter than the hyj)o- 

 stoma; the latter is rather shorter and broader than in A. cancriformis^ 

 and with a swollen area or eminence at the base, not present in A. can- 

 criformis. The antenuse 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 to one-fourth of their length. The 1st 

 ]>air of feet are alike in both sexes. The endites are long and slender, 

 differing only slightly from those of A. lucasanus; the specific defer- 

 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. The 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. wqualis. 



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. lucasaiius, and there are more numerous, finer spines on the 

 under side of the segment next in front of the telson. 



