10 



BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



TANAIS ALASCENSIS Richardson. 



Tanais alascensis Richardson, Proc. U. 8. Nat. Mu.s., XXI, 1899, pp. 819-820; 

 Ann. Mag. Nat. Hist. (7), IV, 1899, pp. 159-160; American Naturalist, 

 XXXIV, 1900, p. 211. 



Locality. — Kyska Harbor, Alaska. 



Depth. — 6-12 fathoms, in sand and mud. 



Body three and a half times longer than ])road. 



Head larg-o, narrowed anteriorly. Frontal margin almost straight. 



First pair of antennae short, stout, consisting of three joints, the tirst 



joint being the longest, and a rudimentary fiagellum 



of two joints. Second pair of antenna more slender, 



a little longer, consisting of five articles, the first 



joint being longest, and a rudimentary fiagellum of 



one joint. Eyes small and pedunculated. 



The first segment of the thorax is confluent with 



the head. The second, third, fourth, and fifth seg- 

 ments increase slightly in length; the fifth and sixth 



are about equal; the seventh is not quite so long as 



the preceding one. 



The abdomen is composed of five segments, the 



first three of which are subequal; the fourth is short, 



about half as long as any of the others and also nar- 

 rower; the terminal segment is as long as the two 



preceding ones together, and is rounded posteri- 

 orly, with a slight median notch. The segments of 



the abdomen decrease in width gradually from the 



first to the terminal segment. The terminal filaments 

 are seven-jointed — the pe- 

 duncle forming the first arti- 

 c 1 e — a n d single-branched, 

 and are furnished at their ex- 

 tremities with a few long 

 hairs. There are three pairs 

 of pleopoda attached to the 

 first three segments. 



The first pair of legs are stout and chelate; 

 the propodus is produced into a strong im- 

 movable finger, irregular in shape, having its 

 central portion raised and truncate on its 

 upper surface, which is distinctly serrate. The 



dactylus is likewise serrate on its inner surface. The other legs are 



slender, with a gradual increase in stoutness. 



Fig. 14.— Tanais alas- 

 censis. a, Dorsal 

 view. X 8. 6, Last 

 joints of leg of the 

 first pair. 



Fig. 13.— Tanais alascensis 

 a, First antenna, x 39. h 

 Second antenna, x 39. 



