344 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 
Genus TIGRIOPUS Norman, 1869 
TIGRIOPUS INCERTUS Smirnov 
PLATE 36, Figures 554-559 
Tigriopus incertus SMIRNov, Trans. Arctic Inst. U. 8. 8. R., vol. 2, p. 205, figs, 16-23, 
1932. 
Twenty-five specimens (U.S.N.M. Nos. 74158 and 78840), including 
both sexes, were obtained in a tow through the kelp about Rat Island 
in the western Aleutian Islands by V. B. Scheffer, of the U. S. Biologi- 
cal Survey, June 26, 1932. They are the first to be obtained since the 
original discovery by Smirnoy off Franz Josef Land. Smirnov’s de- 
scription and figures are correct but rather brief, hence a full descrip- 
tion is here supplied, together with supplementary figures. 
Female.—Metasome elongate-ovate, only a little narrowed posteri- 
orly, the first three thoracic segments with lateral lappets. Rostrum 
wide, spatulate, and curved over ventrally but prominent in dorsal 
view. Urosome narrower than the metasome but two-thirds as wide 
as long, the segments diminishing in length backward. The anal seg- 
ment is quite short and reentrant at the center of its posterior margin, 
but the sinus is not very deep. Caudal rami as wide as long, the long 
inner setae more than twice the length of the entire urosome. 
The first antennae are about as long as the cephalic segment and are 
9-segmented, the four basal segments thick and robust, the five distal 
segments slender and short. Exopod of second antenna 4-segmented, 
with five setae, the end segment the longest and tipped with two un- 
equal setae. Second maxillae broad; hand of chela on maxillipeds 
ellipsoidal, considerably narrowed at each end, the dactylus rather 
weak and reaching only to the center of the hand. First legs prehensile, 
the proximal segment of the exopod as long as the other two segments 
combined, the end segment with four stout curved claws and two 
setae. Endopod with basal segment almost six times as long as the 
other two segments combined, the end segment with two slender claws. 
Fifth legs of the usual pattern, the outer process of the basal segment 
rather large with a long seta, the inner expansions of the two legs 
partially fused on the midline, each reaching the center of the distal 
segment and armed with four setae, the second outer one the longest. 
Distal segment ovate, about twice as long as wide with four setae; the 
terminal one the longest. Total length 1.50 mm. Width of head 
0.52 mm. 
Male.—About the same size as the female but with a somewhat nar- 
rower metasome and urosome. First antenna stout, the terminal chela 
with a globular hand and a reduced clawlike dactylus. Outside of the 
base of the dactylus is a triangular process and a spine, the latter at 
