326 Parainphithoe, Actinacanthus 



and postero-lateral aiigles produced acutely backward; peraeon segmeats 6 

 and 7 and pleon segments 1 and 2 with small intermediate tooth on each 

 side, peraeou segments 1 — 5 with lateral margin deeply carinate. Head, 

 rosti'um ver)' short, sharp, post-antennal corners spiniform. Side-plates 

 with spiniform process. Pleon segmeut 2, postero-lateral corners bidentate. 

 Eyes round, prominent. Antenna 1 about -/•$ as long as antenna 2. Gnatho- 

 pods 1 and 2 slender, subchelate. Telson rather long, entire. 



Arctic Ocean (Point Franklin [arctic Alaska]). Depth 24 m. 



P. cuspidata (Lepech.) 1780 Oniscus cuspidatus, Lepechin in: Acta Ac. Petrop., 

 1778 v.I t. 8 f. 3 I 1877 Acanthozone ciispidata, Miers in: Ann. uat. Hist., ser. 4 v. 19 

 p. 136; V.20 p. 100 1 1888 A. c, T. Stebbincf in: Pep.Yoy. Challenger, u. 29 p.49 (with 

 copy of Lepechin's fig.). 



Perhaps identical with P. hystrix (p. 325). L. 20 mm. 



White Soa. 



3. Gen. Actinacanthus Stebb.*) 



1888 Acanthechinus (Sp. un.: A. tricarinatus) (non P. M. Duncan & P. Sladen 

 1882, Echinodermata!), T. Stebbing in: Rep.Voy. Challenger, r. 29 p. 883. 



Body indurat^d, beset with acute processes (Fig. 74). Head, rostrum very 

 small. Side-plates 1 — 4 acute, 3'^ — 7**^ furnished with acute backward pointing 

 lobes. Antennae 1 and 2. some joints of peduncle with acute projections. 

 Upper lip apically broad, rather uusymmetrically bilobed. Mandible, spine- 

 row abnormal, molar very prominent, palp elongate. Maxilla 1, inner plate 

 with 3 setae, outer with 7 spines, palp long. Maxilla 2, plates broad, outer 

 the broader. Maxillipeds, inner plates well developed, outer rather broad, 

 reaching a little beyond 1^^ Joint of palp, thiuly furnished with setae, 1^* Joint 

 of palp rather longer than 2*^, finger slight, short. Gnathopods 1 and 2 

 (Fig. 75, 76) very long and thin, 5* Joint much longer than subchelate 6*^. 

 finger very small. Peraeopods 3 — 5, 2^ Joint channelled, others decurrent. 

 Üropod 3, rami long, lanceolate. Telson short, entire. Branchial vesicles 

 simple. Marsupial plates long, narrow. 



1 species. 



1. A. tricarinatus (Stebb.) 1883 Acanthozone tricarinata, T. Stebbing in: 

 Ann. nat. Hist., ser. 5 v. 11 p. 205 | 1893 A. t., A. DellaValle in: F. FI. Neapel, u20 

 p. 601 t. 59 f. 11 I 1888 Acanthechinus tricarinatus, T. Stebbing in: Rep. Voy. Challenger, 

 V. 29 p. 884 t. 69, 70. 



Body cylindric, except hinder part of pleon which is a little depressed 

 and strongiy flexed. Peraeon segments 1 — 7 (Fig. 74) each with central and 2 

 lateral acute, 3-sided, serrate, processes connected by transverse ridge ou hinder 

 part of Segment; central process on segment 1 bifurcate, one arm pointing 

 forward, the other backward. Pleon segments 1 and 2 with large central 

 process flanked by 2 tubercles on each side, 3"^ with smaller central process 

 and 1 tubercle. and having a tridentate process rising from bind margin; 

 4*^ with hump, depression, and 2 serrate processes in succession; 5*^ unarmed; 

 6**» with central and 2 lateral processes. Side-plates 1 and 2 pointing 

 forward. tapering, carinate, serrate; 3* and 4"^ with both lobes acute, pointing 

 backward; 7*'' with tlie largest lobe. Eyes not perceived. Antenna 1, l*** Joint 



*) Nora. nov. dKxic, ray, aKavGa, spine. — Tlie name Acanthechinus is preoccupied 

 (1882, P. M. Duncan & W. P.'siaden in : Pal. Ind., ser. 14 p. 34). 



