358 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



extend three-fourths the length of the segment; those of the last two 

 segments extend the entire length of the segment. 



The abdomen consists of three distinct segments, with suture lines 

 on either side of another partly coalesced segment. The third or 

 terminal segment has subparallel sides to about the middle, where the 

 segment gradually becomes narrower to a truncate extremity. On 

 the posterior margin of the terminal segment is a faint indication of a 

 double emargination on either side of an obtuse median point. 



Legs small and slender and devoid of hairs. 



The five small specimens and one large one agree in having the 

 terminal segment as described above. The two larger specimens 

 show the double emargination more distinctly, one of the specimens 

 more so than the other. 



Figures showing all three variations are given. 



The specimens agree in all other characters. 



Dana's specimens were collected by Prof. J. Le Conte on the coast 

 of California. 



IDOTHEA UROTOMA Stimpson. 



Idotea urotoma STIMPSON, Proc. Acad. Nat. Sci. Phila., XVI, 1864, p. 155. MIEKS, 

 Jour. Linn. Soc. London, XVI, 1883, p. 34. RICHARDSON, Proc. U. S. Nat. 

 Mus., XXI, 1899, p. 845; Ann. Mag. Nat. Hist. (7), IV, 1899, p. 264; 

 American Naturalist, XXXIV, 1900, p. 226. 



Locality. Puget Sound. 



Bodj 7 linear, elongate, nearly four and a half times longer than broad, 



4 mm. : 17 mm. 



Head as wide as first segment of thorax and 2i mm. long. Eyes 



small, round, and situated close to the lateral margins. The first pair 



of antennae have the basal article large, dilated; the second and third 

 are small and narrow, subequal; the fourth is 

 clavate. The first pair of antennae extend to 

 the end of the second article of the peduncle of 

 the second pair of antennae. The joints of the 

 peduncle of the second antennas are short and 

 thick; the first article is inconspicuous in a 

 dorsal view; the second and third articles are 

 subequal; the fourth and fifth are subequal and 

 each is about one and a half times longer than 



PIG. 386. IDOTHEA UROTOMA. the third article. Flagellum composed of eleven 



ABDOMEN, x 6i. A- i 



articles. 



The first segment of the thorax has the antero-lateral angles pro- 

 duced to surround the posterior portion of the head, and is shorter 

 in the middle of the dorsal surface than any of the six following 

 segments, which are nearly subequal. The epimera of the second, 

 third, and fourth segments are narrow plates, which in the second and 

 third segments do not quite reach the middle of the lateral margin, 



