54 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxxii. 



Two posterior pairs of thoracic legs longest of all and about equal to each other. 

 All the legs are stout and their liasal segments squamiforni. 



Postero-lateral angle of first abdominal segment rounded, of second and third 

 from obtuse angled to right angled. 



First pair of caudal stylets extending a little farther back than the second; these 

 exceeding slightly the third. The peduncle of the first pair somewhat curved, with 

 the concavity above, the rami equal and two-thirds as long as the peduncle. The 

 peduncle of the second pair little longer than the outer ramus. Inner ramus 

 nearly twice as long as the outer. Third pair of caudal stylets rudimentary, i-onsist- 

 ing of but a single segment. This somewhat longer than the telson, broadly ovate, 

 two-thirds as broad as long and furnished at the tip with two short spines. 



Telson a little longer than wide, narrowing a little to the truncated tip, which is 

 provided at each postero-lateral angle with a couple of stout spines. 



Female. — In the female the propodite of the anterior pair of feet resembles closely 

 that of the corresponding foot of the male. The palmar margin of the second pro- 

 podite is less oblique than in the second foot of the male and does not pass so gradu- 

 ally into the posterior margin. It is also destitute of the jagged edge and the square 

 process of the male foot. There are fewer spines along the margin. One of the 

 spines at the posterior angle is very long and stout. 



This species appears to resemble C. Itennis Smith, but is evidently different. In 

 that species, as descri))ed by Prof. S. I. Smith, the first pair of feet are stouter than 

 the second and have the palmar margin of the propodite much more ol)lique. The 

 reverse is true of the species I describe. Nor do I understand from the description 

 of C tenuis that the posterior caudal stylets each consist of a single segment. There 

 are some minor differences. From C. vitreus, judging from Professor Cope's description 

 in Ainerican Naturalist, Vol. 6, p. 422, \t must differ in the caudal stylets. "Penul- 

 timate segment, with a stout limb with tw^o equal styles," is a statement which will 

 not apply to my species, whichever the '' penuliiinate" segment may be. 



Family ORCHESTIID^]. 



Genus HYALELLA Smith. 



HYALELLA KNICKERBOCKER! (Bate). 



Allorchestes knickerbockerl Bate, Cat. Amphip. Crust. Brit. Mus., 1862, p. 36, 



pi. VI. 

 Hyalella deniata Smith, Rep. U. S. Fish Com., 1872-73 (1874), p. 645, pi. ii. 

 Hyalella inermis Smith, 7th Rept. U. S. Geol. Survey of Colorado, 1873 (1875), 



p. 610. 

 Allorchestes dentatus Faxon, Bull. Mus. Comp. Zool., Ill, 1876, p. 373, figs. 35, 36. ' 

 Allorchestes dentatus yar. inermis Faxon, Bull. Mus. Comp. Zool., Ill, 1876, p. 373. 

 Hyalella inermis Stkbbii<io, Proc. U. S. Nat. Mus., XXVI, 1903, p. 929. 

 Hyalella faxoni Stebbing, Proc. U. S. Nat. Mus., XXVI, 1903, p. 928, pi. lxi. 



Eyes round or nearl}^ so; their distance apart slig'htly greater than 

 their diameter. First antenna shorter than tlie second pair; first and 

 second segments of the peduncle about equal in length, slightly longer 

 than the third; flagellum about twice as long as the peduncle and com- 

 posed of sev^en to nine segments; second antennas about half as long 

 as the body; peduncle exceeding that of the first pair with the two 

 distal segments elongated and nearl}^ equal; fiagelliim usuall}^ but 

 little longer than that of the first pair and composed of eight to fifteen 

 seo-meuts. 



