98 Cumacea: 11. Diastylidae, 1, Diastylis 



longer than rest of limb, joints 5 — 7 subequal. Peraeopod 2, 3^ joint with 

 conspicuous spine on medial margin. 5*^ longer than 6^^ and 7^^^ combined. 

 3*1 and 4*^ pairs without exopods: but as in Diastylopsis (p. 109) 3^ pair 

 distant from 2"^. its 5^^ joint as broad as the 4*'', only a little longer than 

 broad. Peduncle of uropods scarcely longer than the telson; exopod less 

 than %'i^, endopod about half as long, with 1^* joint longer than 2^^ and 

 3^ combined, spines of medial margin respectively 5, 3, 3. L. 9 13 mm, adult 

 d unknown. 



Alaska, lat. 63<^ 'dT N., long. 165^ 10' W., 22 m. 



16. D. rathkii (Kroyer) 1841 Cuma r., Kroyer in: Naturh. Tidsskr., v. 3vi p. 513,. 

 531 t. 5 f. 19— 22; t. 6 f. 17, 18, 23— 30 I 1843 Alauna rostrata, Goodsir in: Edinb. new 

 phil. J., u 34 p. 121, 127 t. 4 f. 1 — 10 | 1846 Cuma rathkii + C- angulata <$, Kroyer in: 

 Naturh. Tidsskr., ser. 2 u2ii p. 144, 207 t. 1 f . 4, 6 ; p. 156, 206 t. 2 f. 1 a— i | 1849 C. r. -\- 

 C. a., Kroyer in: Yoy. Nord Crust., t. 5 f. 1; t. 5 f. 2 | 1852 C. rathkei, W. Liljeborg in: 

 Ofv. Ak. Forh., v.9 p. 6 | 1856 Diastylis rathkii, Bate in: Ann. nat. liist., ser. 2 ». 17 

 p. 451 (3) t. 13 I 1867 Alauna goodsiri (non Bell), A.S.Packard in: Mem. Boston Soc, 

 V. In p. 301 I 1869 Diastylis spinosa (5, A. M. Norman in: Rep. Brit. Ass., t'. 38 p. 271 | 

 1873 D. rathkd. G. O. Sars in: Svenska Ak. Handl., n. ser. u 11 nr. 6 p. 7, D. rathkii, 

 t. 3 f. 8, 9 I 1873 D. orbignyi (?), Latreille MS. in: P. Fischer in: Act. Soc. Linn. Bordeaux, 

 ser. 3 v.Sv p. 425 | 1878 D. himarginatus ^ , Bate in: Ann. nat. Hist., ser. 5 v.l p. 409 | 

 1878 D. fc., Sim in: Ann. nat. Hist., ser. 5 v. 2 p. 453 j 1879 D. b.. Bate in: Ann. nat. 

 Hist., ser. 5 u3 p. 93 | 1879 D. rathkii, A.M.Norman in: Ann. nat. Hist., ser. 5 v.'6 p. 54 | 

 1880 D. Rathkei, Stuxberg in: Bib. Svenska Ak., v. 5 nr. 22 p. 35 (distribution, numbers) | 

 1883 Cuma rathkii, Burmester. Beitr. Cuma, p. 1 1. 1, 2 | 1885 C. r., H. Blanc in: Recu. 

 zool. Suisse, v.2 p. 253 t. 10 (development of egg) | 1900 Diastylis rathkei, G-. 0. Sars 

 in: Crust. Norway, u 3 p. 44 t. 33, 34, D.r. var. cj, p. 107 t. 70— 72 | 1900 D. rathkii, Zimmer 

 in: Fauna arctica, v.l p. 423 (with extensive synonymy), 434, D. r. var. glabra, Zimmer, 

 p. 425 1 1901 D. r., Ohlin in: Bih. Svenska Ak., 11 26 nr. 12 p. 46 | 1902 D. r. var. sarsi, A.M. 

 Norman in: Ann. nat. Hist., ser. 7 ^3.10 p. 478 | 1906 D. rathkei, A. M. Norman & T. Scott,. 

 Crust. Devon Cornwall, p. 30 | 1909 D. r., Stappers in: Cellule, ?;. 25ii p. 351, 358 t. 1 

 f. 9; t. 2 f. 1—18 (le tube digestif) | 1909 D. r.. A. M. Norman & ft. S. Brady in: Nat. 

 Hist. Tr. Northumb., n. ser. 2 u 3ii p. 29 | 1911 D. rathkii, Stappers in: Camp. arct. 

 Orleans, Crust. Malac. p. 110 (distribution) | 1912 D. r., Caiman in: P. U. S. Mus., vAl 

 p. 605, 652. 



Variable with the variations ill defined. Q . Body slender. Pseudorostral 

 lobes horizontal, conical, antero-lateral corners distinct or almost obsolete,, 

 serrate ; frontal lobe of carapace with double row of forward pointing denticles 

 down the middle, sometimes crossed by 1, 2 or 3 imperfect transverse rows, 

 and flanked by scattered denticles, sometimes few^, sometimes very numerous, 

 Pedigerous segment 5 serrate in front, postero-lateral angles acute, strongly pro- 

 duced straight backwards or slightly divergent. Pleon segments simple, smooth, 

 telson shorter than peduncle of the uropods but reaching its end or equal to it, the 

 narrow section elongate with about 15 or fewer pairs of lateral spinules. the apical 

 pair short. J]ye small, distinct. Antenna 1, l^* joint with or without small 

 apical tooth, longer than 3*1, 3^ than 2"^. Antenna 2, the joints short, 

 successively shorter. Peraeopod 1, 2'"' joint scarcely longer than rest of limb, 

 Avith denticles on side of distal part, joints 5 — 7 subequal. Peraeopod 2,. 

 7*^1 joint much or not much longer than 6^^, 5'^'^ much longer than both 

 combined. 3*^ and 4*'^ pairs stout, setose, without exopods. Exopod of 

 uropods about half as long as the peduncle, longer than the endopod, of 

 which the 1"** joint is longer than the other 2 combined, spines of the 

 medial margin respectively 6, 3, 2 or 3. Colour whitish with carneous tinge, 

 L. 17 mm. 



