SMITH.] ZOOLOGY AMPHIPOD CRUSTACEANS. 609 



nearly as long as the basal, slender, tapering, and furnished with a few- 

 slender setse at the tip. TelsoQ stout, as long as broad ; the posterior 

 margin rounded and furnished each side with a slender seta. 



Length ^rom front of head to tip of telson, 3.5™"^ to 5.8™™. 



Colorado, 1873 ; Carpenter, collector. 



It also occurs in Norway, Maine (S. I. Smith) ; Salem, Mass. (Caleb 

 Cooke) ; New Haven, Conn., in small ponds of stagnant water (Pro- 

 fessor Verrill, S. I. Smith) ; Madison, Wis. (Professor Verrill) ; Madeline 

 Island, Lake Superior,, (J. W. Milner) ; West Fork of the Desmoines 

 Eiver, Humboldt, Iowa (Caleb Cooke) ; Lake Raymond, Nebraska (T. 

 M. Prudden and O. Harger) ; Bird wood Creek, Nebraska (O. Harger)^ 

 The Dalles, Oregon (O. Harger). 



Hyalella inermis, sp. nov. (Plate I, E'igs. 1-2.) 



Closely allied to the last species, but wholly without teeth upon the 

 dorsal margin of any of the abdominal segments. Two specimens, 

 male and female, give the following additional characters : 



Male: Antennula reaching to tbe middle of the flagellum of the 

 antenna ; ultimate segment of the peduncle fully as long as the penul- 

 timate ; flagellum considerably longer than the peduncle, and composed 

 of eight articulations. Flagellum of the antenna much longer than the 

 peduncle, or than the flagellum of theantennuhi. First pair of thoracic 

 legs almost exactly as in the last species. The second pair of thoracic 

 legs (Fig. 2, terminal portion) are much smaller in i)roportion than in 

 the last species ; the palmary margin is transverse, nearly straight, and 

 wholly without an emargiuation in the middle; the dactylus slightly 

 curved and terminating in an acute horny tip. The remaining thoracic 

 legs, the caudal stylets, and telson as in the last species, or, if diifering 

 at all, only very slightly. 



The second pair of thoracic legs are very different from those of the 

 adult males of H. dentafa, but resemble much more those of the young 

 males of tnat species (Fig. 4), and it is possible that, in our single speci- 

 men, they are reproduced appendages, and not fully developed. This 

 seems quite improbable, however. The proportional size and other 

 differences are well shown in Figs. 2, 3, and 4, which are all enlarged 

 the same amount. \ 



The female (Fig. 1) differs very little from the female of H. dentata, 

 except in the absence of dorsal teeth upon the abdomen and in the 

 same, or nearly the same, slight diflerences in the antennulss and anten- 

 nae, which seem to characterize the male. 



Length from front of head to tip of telson, male, 5.5™™ ; female, 6.0™™. 



Colorado, 1873; Carpenter, collector. 



Gammarus limn^us. (Plate II, Figs. 13-14.) 



Gammarus lacustris Smith, American Journal of Science, III, vol. ii, p. 4.53, 1871; 

 and Preliminary Report on Dredging in Lalie Superior, in Report of tbe Chief 

 of Engineers, 1871, p. 1023, 1871. 



Colorado, 1873 ; Carpenter, collector. Cool Spring, Fire-Hole Basin 

 (No. 224). Lake near Long's Peak ; elevation, 9,000 feet ; June 1, 1873. 



The first and second pairs of thoracic legs are quite characteristic of 

 this species. The palmary margin of the first pair, in the male (Fig. 13), 

 is slightly convex and continuous with the posterior margin ; has a nar- 

 row lamellar edge, and is armed with a few long hairs and usually two 

 long, obtuse spines near the middle of the margin, and three or four 

 smaller ones near the tip of the closed dactylus. In the female, the pro- 

 podus is considerably smaller and shorter in proportion than in the male; 

 S9 GS 



