Acidostoma, Acontiostoma 15 



Differs from A. obesum iu the followiug points. Pleon segment 3, 

 postero-lateral angles slightly projecting, but not acute. No eyes (small eyes, 

 with a little biconvex Cornea, Della Valle). Uropod 3 with the rami almost 

 tubercular, scarcely reaching beyond peduncle of uropod 2. Telson almost 

 quadrate, slightly emarginate distally. Colour whitish (orange-yellow, Della 

 Valle). L. 9 11, cJ 7-5 mm. 



Arctic Ocean (Lofoteu Isles), depth 800 — 1200 m; ? Mediterranean, on Cereactis 

 aurantiaca (Chiaje). 



4. Gen. Acontiostoma Stebb. 



1888 Acontiostoma (Sp. typ.: A. marionis) (part.), T. Stebbing in: Rep. Voy. 

 Challenger, v. 29 p.-709 | 1893 A., A. Della Valle in: F. Fl. Neapel, ».20 p. 785. 



Body compact (Fig. 4) ; side-plates large, deep, 1^* pair projecting over 

 sides of head. Antenna 1, 2^ Joint not extremely short, both flagella with 

 few and very short joints, only in ö 1^* of primary enlarged and fringed 

 with filaments. Upper lip with pointed apex. Lower lip with the lobes 

 narrowed. Mandible long and narrow, without molar, palp slender, much 

 shorter than the trunk. Maxiila 1, inner plate small, 

 narrow, outer plate narrow with serrate spines, palp small, 

 distinct, 1-jointed. Maxiila 2, both plates narrow. Maxillipeds, 

 the basal part robust, inner plates narrow, apically acute, 

 outer plates apically angular, without marginal teeth, palp 

 geniculate, scarcelv reaching beyond outer plate, P^ Joint 

 Short, 2d and 3^ long, 4«^ small. Gnathopod 1 slender, ^'^'Lat^kiTiew'''^' 

 not subchelate, 5**^ Joint shorter than 6*^^. Gnathopod 2 

 with 6*^ and 7* joints forming a feeble chela. Peraeopods 3, 4 and 5 robust, 

 2^ and 4*^1 joints much expanded. Uropod 3 very short, without rami. 

 Telson short, entire or emarginate. 



2 species. 



Synopsis of species: 



Integument solid, opaque ■ . . . . 1. A. marionis . . . . p. 15 



Integument thin, pellucid 2. A. magellanievQn . p. 15 



1. A. marionis Stebb. 1888 A. m., T. Stebbing in: Rep. Voy. Challenger, ??. 29 

 p. 709 t. 30 I 1893 A. m., A. Della Valle in: F. Fl. Neapel, «;.20 p. 786. 



Pleon Segments 1 — 3 distally carinate on the back, 4**^ with depression 

 followed by elevated carina produced a little backward. Eyes large, oval. 

 Antenna 1, 1*** Joint as long as rest of antenna, 2^ as long as the 7-joiuted 

 flagellum, accessory flagellum 2-jointed. Antenna 2 little longer than antenna 1, 

 ultimate Joint of peduncle much shorter than penultimate, a little shorter 

 than the 7-jointed flagellum. Mandible with spine-row of 3 or 4 spinules, 

 and in place of molar a ciliated ti'act. Maxilla 1, palp small, acute, 

 1-jointed. Maxillipeds, inner plates short, 4*^ Joint of palp very short, with 

 small oval spine within the tip. Gnathopod 2, o^^ Joint a little longer 

 than 6*'!. Uropods with many spines. Telson not much longer than 

 broad, apex rounded, girt with short spines. L. 7*5, height at centre rather 

 over 5 mm. 



Southern Indian Ocean (Marion Island). Depth 90 — 135 m. 



2. A. magellanicum Stebb, 1888 A.m., T. Stebbing in: Rep. Voy. Challenger, 

 i;.29 p. 714 t.31. 



