Pacific Coast of North America. 



159 



Fi-. 1. 



Analytical Key to the Species of Tanais. 



a. Inferior antennae scarcely half the length 



of superior antennae. Pereiopoda 



having the first three joints short and 



broad, affixed to sides of pereion like 



plates of mail 1. T. loricatus, Spence Bats, 



a'. Inferior and superior antennas of nearly 



equal length. Pereiopoda with joints 



not dilated, slender 2. T. alascensis, sp. n. 



1. Tanais loricatus, Spence Bate. 



Tanais loricatus, Spence Bate, Lord's Naturalist in British Columbia, 

 ii. (1866), p. 282. 



Hah. Esquimault Harbour, British Columbia. 



2. Tanais alascensis, sp. n. 



Body three and a half times longer than broad. 



Head large, narrowed anteriorly. Fron- 

 tal margin almost straight. First pair of 

 antenna short, stout, consisting of four 

 joints, the first joint being the longest. 

 Second pair of antennas more slender, a 

 little longer, consisting of four joints, 

 the first joint being longest, and a rudi- 

 mentary flagellum. Eyes small and 

 pedunculated. 



The first segment of the thorax is con- 

 fluent with the head. The second, third, 

 fourth, and fifth segments 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 seg- 

 ments, the first three of which are sub- 

 equal ; 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 posteriorly, 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 and single- 

 branched, and are furnished at their ex- Tanais alnscensis,a^.n. 

 tremities with a few long hairs. x 8. a, dorsal view ; 



The first pair of legs are stout and f^iofthlfirif "^- °^ 

 chelate ; the propodus is produced into a ^° 3 p . 



12* 



a 



ir 



