I8OPODS OF NORTH AMERICA. 495 



SO. Genus ILYARACHNA G. O. Sars. 



Body compact, attenuated behind, with a strongly marked median 

 constriction. 



Head very large and broad, transversely truncated in front, lateral 

 parts greatly expanded. First pair of antennae with flagellum not 

 much elongated. Second pair of antennae longer than the body. 

 Mandibles with molar expansion; cutting edge not divided; palp 

 feeble. 



The first four segments of the thorax crowded together and slightly 

 excavated transversely; last three segments large and convex, the fifth 

 segment scarcely narrower than the preceding segments. 



Terminal segment of body narrow and triangular. 



First pair of legs small, simple; second pair larger; two following 

 pairs slender and elongated; first two pairs of natatory legs of similar 

 structure; carpus expanded, cordiform, propodus much narrower, 

 oblong, dactylus well developed; last pair much narrower with carpus 

 but slightly expanded, propodus linear, dactylus elongated. 



Uropoda small, biarticulate. 



ILYARACHNA HIRTICEPS G. O. Sars. 



Hyarachna hirticeps SAKS, Forh. Vid. Selsk. i Christiania, 1869, p. 167, 1870. 

 HANSEN, Vid. Medd. naturh. Foren. i Kj0bh., 1887-88, p. 195. SARS, Crust, 

 of Norway, II, 1899, p. 137, pi. LX. RICHARDSON, American Naturalist, 

 XXXIV, 1900, p. 301; Proc. U. S. Nat. Mus., XXIII, 1901, p. 560. OHLIN, 

 Bihang till K. Sv. Vet.-Akad. Handl., XXVL Afd. iv, No. 12, 1901, pp. 

 35-36. 



localities. Latitude 66 32' north, longitude 55 34' west; latitude 

 71 10' north, longitude 58 56' west; latitude 72 41' north, longitude 

 59 50' west. (Greenland.) 



Depth. 100-227 fathoms; 20 to 435 meters (Ohlin). 



"Body of a similar appearance to that in the type species, but more 

 than twice as large, and somewhat more robust. Cephalon very broad, 

 with the dorsal face strongly vaulted, and densely clothed with short, 

 stout bristles. Anterior edge of the first four segments of mesosome 

 very distinctly elevated, and minutely crenulated throughout; lateral 

 parts of first segment imperfectly developed. The three posterior 

 segments of mesosome combined about the length of the preceding 

 part of the body; the anterior segment evenly emarginated behind. 

 Caudal segment of a similar form to that in /. longicornis. Superior 

 antennae comparatively short, not nearly reaching to the middle of the 

 penultimate peduncular joint of the inferior ones, basal joint armed 

 along the inner edge with scattered denticles, flagellum, in female, not 

 attaining the length of the last two peduncular joints combined. 



See Sars for characters of genus, ("rust, of Norway, II, 1899, pp. 134-135. 



