^•"- ^■'"- FRESH- WA TER OSTJi. I ('(jD. I -SI/ A liPE. 



Furoa almost straight, about twent3^-three times as lono- as w jdc aiul 

 very faintly toothed on dorsal nuirgin for about oii(>-half its Icncrtli 

 (%•• 5). _ 



Terminal claw straight, rather stout, nearly smooth, and one-lialf as 

 long as furca. Subterminal claw four-sevenths length of terminal one 

 and straight. Terminal seta very slender, two-thirds length of dorsal 

 one, which is slightly more than one-half as long as subterniinal <la\v. 

 No males seen by me. 



Described from several specimens which wcit' sent to the Inited 

 States National Museum by Dr. E. Palmer from Durango, Mexico. 

 Received by the Museum 8eptem])er 11, 1897. Accession No. 3255!». 



But one other species has been reported from America, ('. mfmi 

 (Saussure), which differs from the above in the form of the shell, 

 furca, and other minor details. In C. azteca the ratio of length to 

 Itreadth of furca is as IT to 1, while in O. mexicmui this ratio is al)()ut 

 as 2-1 to 1; moreover, its entire dorsal margin is faintly ciliate in ('. 

 azteca, while but about one-half this edge is faintly toothed in C 

 mexicana. 



2. CHLAMYDOTHECA AZTECA Saussure. 



Plate LXIX, figs. 1-4. 



Cijpria ( Chlaimidotheca) azfeca Saussure, Memoire sur divers erustaces iiouveaux 

 des Antilles et du Mexique, Mem. Soc. Piiys. et Nat. Geneve, 1858, p. 487, 

 pi. VI, figs. 45-54. 



Length, 3.3(> mm.; height, 2 mm.; width, 1.80 mm. 



One of the largest forms of this genus known, uniformly yellowish 

 gray in color, with occasionally a dark patch posteriorly. Shell smooth 

 and glistening to the naked eye, but shown to be quite thickly covered 

 with small papillar elevations by using a one-fourth-inch objective. 



Seen from the side (tig. 1) the shell is highest at the posterior one- 

 third, sloping rather abruptly to the posterior lower angle, which is 

 provided with a small hyaline flange. 



Seen from above (tig. 3), as in ('. viextcana, the shell is widest at the 

 posterior one-third, bluntly rounded posteriorly, and wedge-shaped 

 anteriorly. There is a very noticeable hyaline flange, fringed with 

 hair, on the anterior margin. Ventral margin nearly straight, (^xcept 

 for a sinus at its union with the anterior flange. 



Natatory setffi of the second antenna^ plumose, n^aching to tips of 

 terminal claws. Termuial claws stout, slightly curved, the longest 

 a])out six times as long as the terminal segment, or live-fourths that of 

 the last two segments. As in C. mexicaini, the second segment of the 

 flrst pair of feet is provided with two setj^ at its distal angh- a most 

 prominent generic character. 



Second foot not especially different from that of C m.. ,■...,„<,. 

 Furca almost straight, from is to 20 times as long as wide, and famtly 

 pectinate on almost entire dorsal margin (flg. -1). 



