ISOPODS OF NORTH AMERICA. 11 



Color brown, marked in some specimens with a darker brown, and 

 having oval patches of the darker color on the head. 



Kyska Harbor, Alaska; Dr. W. H. Dall, collector; depth, 6 to 12 

 fathoms. 



Type. Cat. No. 22563, U.S.N.M. 



TANAIS ROBUSTUS Moore. 



Tanais robustus MOORE, Proc. Acad. Nat. Sci. Phila., 1894, pp. 90-94, pi. v. 

 RICHARDSON, American Naturalist, 1900, XXXIV, p. 211; Proc. U. S. Nat. 

 Mus., 1901, p. 501. 



Locality. New Jersey. 



Found "inhabiting minute tubes in the crevices between the scales 

 of the turtle's (Thdlassochelys caretta) carapace. When unmolested 

 these little crustaceans could be seen crawling carefully about among 

 their fellow voyagers or lying at the mouths of their domiciles with 

 only the head and chelae projecting; when disturbed they promptly 

 retreated out of sight. " MOORE. 



"It is quite robust for the family, being less than 3i times as long 

 as broad. The carapace, which is the broadest portion of the body, 

 is terminated anteriorly by a minute rostrum, whilst its posterior border 

 is somewhat concave in the middle line. In front of the origin of the 

 great gnathopods the lateral outline is strongly concave, but opposite 

 the bases of these limbs it becomes swollen. When viewed dorsally, 

 the carapace appears in general figure top-shaped. Two grooves, one 

 on each side, indicate upon the dorsal surface the inner boundary of 

 the branchial chamber. Behind the carapace the breadth of the body 

 becomes gradually less with each successive segment. The fourth free 

 segment of the peraeon is the longest, slightly exceeding the third, 

 which is in turn longer than the fifth. 



"The pleon is composed of six distinct segments, of which the 

 fourth and fifth are much shorter than the others and the sixth is 

 terminated posteriorly by a blunt median projection. The body is 

 constricted at the joints and. the segmentation is distinctly marked. 

 The dorsal surface is furnished laterally with a few setae, which on 

 the first and second segments of the pleon form a short row on each 

 side, but never form a transverse band crossing the segment. 



"The e} T es and eye-lobes are large, the latter being let into deep 

 recesses in the anterior lateral portion of the carapace. 



" The an tennulae consist of three joints, of which the basal one is 

 somewhat longer than the other two combined. A small knob (rudi- 

 mentary flagellum) terminates each. In the male the an tennulae usually 

 about equal in length the carapace with the first free segment, but are 

 sometimes considerably longer. In the female they are about equal 

 to the carapace alone. 



