322 GEOLOGICAL SURVEY OF THE TEEEITORIES. 



the lateral spines are minute ; along tlie middle line are five spines ; 

 the lateral groui^ near the base are arranged more in a line than in A. 

 longicaudatiis, where they form a more irregular group. The under sur- 

 face is nearly smooth compared with A. longicaudatiis 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. Inoigicaiidatus 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. ]Srumber of abdominal segments beyond 

 hind edge of carapace, 29 ; number of segments behind the last pair of 

 appendages, 11. 



Total length of carapace, 25'°'" j length along the middle, 19^'"'"; 

 breadth, 21"™. 



Length of dorsal keel of carapace, 12^'"'" ; from front end of keel to 

 front edge of head, T^-""". 



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 cara- 

 pace, and shorter abdomen with its longer telsou. It need not be con- 

 founded with A. wqualis, 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 Eocky Mountain plateau and to Texas and Mexico. 

 It diiiers chiefly from A. longicaudatus and A. lucasanus in the shorter 

 endites and much longer, smoother telson, and the smooth, almost 

 hairy, instead of spinj^ caudal ai^pendages, 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 dilfer, nor do the appendages. 



Apus lucasanus Packard. 



Plates XVI, figs. 2, 2a, 26 ; XVIII, figs. 3, 5 ; XIX, figs. 1, 5 ; XXI, figs. 7, 8, 10, 12, 13. 



Apus lucasanus Pack., Amer. Journ. Sc. Aug., 1871. Bull. IJ. S. 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. Antennae as in A. 

 longicaudatus. The 5th endite of 1st 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, PI. XVI.) The first pair of feet and succeed- 

 ing appendages are shorter and rather smaller than in A. longicaudatus. 

 In the 1st 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, 



