Ckl STAil \ MU.tUKtTRACA. III. 



75 



Macrostylis ci. o. Sars. 



Sars has published a useful diagnosis of this most characteristic genus in his standard work; 

 he had, however, only a single species, ,!/. spinifrra G. O. Sars, but in the appendix he added a second 

 species, M. d'anai longirrmu Mein. A third species, M. latifrons Redd., was secured by the "Chal- 

 lenger" in the North Pacific. But the genus is evidently rather rich, as I have six species, four among 

 them new, from the "Ingolf area, and, besides, fragments of a seventh form. The new forms agree 

 in most of the features pointed out by Sars as being of generic value with his M s/nni/rra, but a 

 couple of characters, viz. his statement on the female operculum and on the uropods, must be dropped, 

 while some other features can be pointed out An examination of the structure with special reference 

 to generic characters may be of some interest 



The body is somewhat or considerably elongate, to some extent similar in all species. Heail 

 movable. Eyes wanting. Antennula* short, at most 5-jointed, in the males with more sensory filaments 

 and, besides, sometimes thicker than in the female. Antennae with 5 free joints in the peduncle, while 

 the basal joint is very short and frequently scarcely distinguishable; squama seems to be wanting. 

 The mouth-parts are well figured by Sars; the mandibles have the incisive part, the movable lacinia, 

 and the sete well developed, the molar process strongly tapering to the narrow, obtuse, setiferous end 

 and directed considerably backwards; palp wanting. Maxillipeds (PI. VII, fig. 4C, and Sars, PI. 51) with 

 second joint long and more than twice as long as broad, with its lobe oblong; palp with second joint 

 broad and long, third joint broad and short the two distal joints short or nearly rudimentary; epipod 

 very long. 



The three anterior thoracic segments constitute together a separate subquadrangular section, 

 with each lateral margin forming a nearly uninterrupted, distinctly convex line; these segments arc 

 dorsally well marked off, but yet scarcely, or at most slightly, movable; the four posterior segments 

 are quite different each very movable, but the articulation between seventh segment and abdomen 

 seems to be slightly movable in some forms. 



The legs have been well figured and described by Sars; the basal joint of most pair* i- distinct 

 but without any process; the three anterior pairs increase somewhat in length and very conspicuously 

 in thickness and number of spines from first to third pair, the last-named pair having third and fourth 

 joints somewhat or considerably expanded and seeming to be "fossorial in character"; fourth pair are con- 

 siderably shorter and thinner than third or second pair, and adapted for walking; from fourth to sixth 

 or seventh pair the legs increase much in length; second joint of seventh pair has a row of probably 

 natatory setae along a part of the posterior margin of both margins (PI. VII, fig. 3 e(. 



The abdomen is more or less oblong-quadrangular, with the posterior margin convex and the 

 uropods inserted on the outer angles; a tergite of a basal segment was not found, but its sternite is 

 distinct in some species. When the abdomen is examined from above, and is not too opaque, a pecu- 

 liar organ is seen shining through the integument (PI. VII, figs, i c, 3 f and 4 f; PI. VI, fig. 6c) near 

 the lateral margin somewhat before its end; each organ is a cavity narrowing backwards as a duct, 

 which seems to open at the inward angle of the uropod; the central part of the cavity is filled with 

 a lump of minute rounded or angular crystals. -- On the lower side of the abdomen the operculum 



