OCR Text |
Show 304 DR. H. J. HANSEN ON THE [Nov. 29, nearly as long as the maxillulse, rather slender; the lobe from the second joint oblong, as long as the two lobes from the third joint. Maxillipeds (fig. 3 h) Large; second joint-the lobe not taken into consideration-very large, more than twice as long as broad, its lobe, which is marked off by a transverse suture, is large, longer than broad, with several small hooks at the inneft* margin, while the distal margin is cut off and furnished with several short setae, some of which are very broad, scale-like; fourth and fifth joints rather expanded; the two distal joints slender. Epipod very long, about three times longer than broad. Basal joint in the adult female without any leaflet directed into the marsupium. Thorax shaped nearly as in Ianira; anterior lateral angle of first segment always produced into a triangular, acute, flat process directed forward *. First pair of legs terminates in a prehensile hand, the sixth joint being large, compressed, with the palmar margin armed with processes or remarkable spines or setae, while the seventh joint together with its short terminal claw is slender and claw-shaped; this hand shows sometimes rather little, but often a highly developed, sexual difference, being frequently not only much larger in the adult male than in the female, but of quite another shape. The six other pairs of legs essentially as in Ianira ; seventh joint terminates in a claw, beneath which a spine of the same size is seen. Marsupial lamellae four pairs, proceeding from first to fourth pair of legs. Abdomen essentially as in Ianira ; two rudimentary segments are observed in front of the large abdominal shield; the latter has at the end of each lateral margin a small notch, the outer margin of which is formed by a sharp triangular tooth. Pleopoda are exceedingly characteristic +. In both sexes the third pair is only to a very small extent (PI. XIX. fig. 1 cl) covered by the first pair (in the female) or the two anterior pairs (in the male); its sympod is rather small, quadrangular (PL XX. figs. 2 i and 2 n) ; the two-jointed exopod is exceedingly large, scarcely respiratory, and covers the respiratory endopod, which is unjointed and several times smaller; the inner margin of each exopod is straight, and the two exopods touch each other along the mesial line, constituting together a kind of operculum which covers the lower surface of abdomen, with the exception of a moderately broad margin at the sides and behind, and a small portion in front occupied by the anterior pleopoda. In the female the pleopoda of the first pair are completely fused (PL XX. fig. 2 m ; PL XXI. fig. 2 i), constituting a subtriangular more or less oblong operculum, which is at least three times smaller than an exopod of the third * According to Haswell this process is wanting in S. inerme Hasw., but in the sequel it is shown that this species probably does not belong to the genus Stenetrium. f In Section V . of this paper the comparative morphology of the pleopoda in the Asellota is discussed; in this account of Stenetrium and in Sections I I I. and IV . the structure of the pleopoda is described and the interpretations applied without explanations. |