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Show 1 9 0 4 .] ASELLOTA-GROUP OF CRUSTACEANS. 3 0 3 later years. In tlie following pages I describe six species examined by myself of this type, five of which are considered new to science. Having now such a rich material of an important and imperfectly known genus at my disposal, I thought it appropriate to work it out; besides, I seize the opportunity of elucidating some points of the morphology of the pleopoda in other Asellota, and discussing the classification of the whole group. II. Description of the Genus Stenetrium Uasiv. Body oblong, three or four times as long as broad, rather depressed, shaped nearly as in Ianira. Head with the dorsal surface much broader than long; in advance of the anterior margin is seen a transverse area, the frontal plate (PL XIX. fig. 1 a, f ) , between the insertions of the antennulae. When the head is stretched forward a large, sloping, anteriorly rounded part is seen in advance of the frontal plate ; this area is clypeus and labrum, and when the mandibular palps are in their natural position the distal part of their second joint and the whole third joint are observed on the surface of the clypeus. Eyes always distinct, but varying much as to shape, size, and situation. Antennulae from somewhat shorter to a little longer than the breadth of the head. Peduncle three-jointed ; basal joint oblong but rather thick, longer and much thicker than any of the two others. Flagellum varies much in length and number of joints. Antennas nearly as long as or a little longer than the body, very similar to those in Ianira. The peduncle consists of four short and two long joints: the first joint is always well developed (and shows excellent specific characters); third joint on the outer side with an exopod which is a subtriangular, oblong, setiferous plate, with the lateral parts bent inwards. Mouth-parts essentially as in Ianira. Mandibles (PL XX. fig. 3 a) moderately long; lacinia mobilis of the left mandible (fig. 3 b) consists of a thick, long, movable process and a few very broad, long, a little curved setae, pectinate with exceedingly short teeth along their anterior margin; one of these setae proceeds from the process itself near its base; the articulating membrane is broad on the lower side. Lacinia mobilis of the right mandible (fig. 3 c) shows a number (in >$. antillense about ten) of very thick setae, nearly all with saw-teeth. Mandibular palp well developed, three-jointed; terminal joint rather broad and long, with a comb of numerous fine seta?. Hypopharynx (paragnatha) (Pl. XX. fig. 3 d) rather deeply bifid; each half has the inner margin nearly straight and clothed with fine bristles on its distal part; the anterior angle rather rounded and the outer margin very convex.-Maxillulae (fig. 3 e) slender ; the inner lobe terminates in three curved, thick, plumose setae ; outer lobe (fig. 3 / ) with a good number of very thick, curved spines, coarsely serrate along at least one margin. Maxillae (fig. 3 g) |