ISOPODS OF NORTH AMERICA. 7 



2. Genus TANAIS Audouin and Ed-wards. 



Eyes present and well developed. Abdomen composed of five or 

 six segments. Only three pairs of pleopoda present, all fully devel- 

 oped. Uropoda simple, single-branched. Incubatory pouch formed 

 of two lamellae issuing from the base of the fifth pair of legs. Man- 

 dibles strong with the molar expansion well developed. 



ANALYTICAL KEY TO THE SPECIES OP THE GENUS TANAIS. 



a. Pereiopoda having the first three joints short and broad, affixed to the sides of 

 the pereion like plates of mail. Inferior antennae scarcely half the length of the 



superior antennae Tanais loricatus Spence Bate 



a' . Pereiopoda with joints not dilated, slender. First and second antennae of nearly 



equal length. 



6. Abdomen composed of five segments. 



c. Uropoda composed of three articles, a basal article, and a bi-articulate branch. 

 First and second abdominal segments with transverse setiferous bands. 



Tanais cavolinii Milne Edwards 



</. Uropoda composed of seven articles, a basal article, and a branch composed 

 of six articles. First and second segments of abdomen without setiferous 



bands Tanais alascensis Richardson 



V. Abdomen composed of six segments. 



c. Uropoda composed of four articles, the peduncle, and a branch composed of 

 three articles. Body robust. Last three segments of abdomen not abruptly 

 narrower than three preceding segments. Posterior end of head about two 

 and a half times wider than anterior end. First pair of legs with chelae 

 strong and powerful, the dactylus strongly arched, finger and thumb widely 



separated in male Tanais robustus Moore 



(/. Uropoda composed of six articles, the peduncle, and a branch composed of 

 five articles. Body narrow, elongate. Last three segments of abdomen 

 abruptly narrower than three preceding segments, about half as wide. 

 Posterior end of head not greatly wider than anterior end. First pair of 

 legs with finger and thumb not widely separated. 



Tanais normani Richardson 



TANAIS LORICATUS Spence Bate. 



Tanais loricatus SPENCE BATE, Lord's Naturalist in British Columbia, II, 1866, 

 p. 282. RICHARDSON, Proc. U. S. Nat. Mus., XXI, 1899, p. 819; Ann. Mag. 

 Nat. Hist. (7), IV, 1899, p. 159; American Naturalist, XXXIV, 1900, p. 210. 



Locality. Esquimault Harbor, British Columbia. 



Found in the hollow of a sponge. 



"Exemplum imperfectum; inferiores antennas semi-breviores quam 

 superiores habens; gnathopodum primi paris propoda ovata dactylo 

 breve et tumido; periopodum primis tribus articulis brevibus et latis 

 sunt, loricis ad pereionem adherent! bus. 



"The only specimen in the collection is imperfect. The first seg- 

 ment of the pereion appears to be imperfectly fused with the cephalon; 

 inferior antennse scarcely half the length of the superior. First pair 

 of gnathopoda having the propodus ovate; dactylos short and tumid, 

 shorter and less pointed than the digital process of the propodos. 



