\ 



ISOPODS OF NORTH AMEKICA. 495 



80. Genus ILYARACHNA G. O. Sars.« 



Body compact, attenuated l)ehiiui, with a stionoly marked median 

 constriction. 



Head very laryc and ))road, transversely ti'uncated in front, lateral 

 parts greatly expanded. First [)air of antenna^ with llaoelhnn not 

 nnich elongated. Second ])air of antenna^ longer than the Ixxly. 

 Mandibles with molar expansion; cutting edge not divided; palp 

 feehle. 



Th(^ first four segments of the thorax crowded together and slightl}^ 

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

 segment scarcely narrower than the ])receding segnuMits. 



Terminal segment of body narrow and triangular. 



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

 pairs slender and elongated; lirst two pairs of natatoiy legs of similar 

 structure; carpus expanded, cordifoi-m, propodus nuich narrower, 

 oblong, dactylus well developed; last i)air much narrower with carpus 

 but slightly expanded, propodus linear, dactylus elongated. 



Uropoda small, biarticulate. 



ILYARACHNA HIRTICEPS G. O. Sars. 



Ryarachna hirticeps Sars, 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.— Ohlix, 

 Bihang till K. Sv. Vet.-Akad. Handl., XXVI, AM. iv, No. 12, 1901, pp. 

 35-36. 



Localities. — Latitude 06^ 32' north, longitude 55° 34' west; latitude 

 71° 10' north, longitude 58- 5»)' west; latitude 72^ 41' north, longitude 

 59° 50' west. (Greenland.) 



Depth.— \m-'2Ti fathoms; 20 to 135 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 strong!}' vaulted, and densely clothed with short, 

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

 yery distinctly elevated, and minutely crenulated throughout; lateral 

 parts of first segment im])erf«>ctly developed. The three po'sterior 

 segments of mesosome combined about the length of the preceding 

 part of the body; the anterior segment evenl}^ emarginated behind. 

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

 antennjc 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. Hagellum, in female, not 

 attaining the length of the last two peduncular joints combined. 



"See Sars for characters of genus, Crust, of Norwaj', II, 1899, pp. 134^135, 



