64 Rev. A. M. Norman on Crustacea Cumacea. VI. — Crustacea Cumacea of the l Lightning ,' 'Porcupine, 1 and ' Valorous ' Expeditions. By the Rev. A. M. NOR-MAN, M.A. Order CUMACEA. Genus Diastylis, Say, 1817. (=Alauna, Goodsir, 1843.) 1. Diastylis Rathhii (Kroyer). 1841. Cuma Rathhii, Kroyer, Naturkist. Tidsskrift, vol. iii. p. 513, pi. v. figs. 17-30; id. op. cit. anden rsekkes ii. 1846, p. 144, pi. i. figs. 4, 5; id. Voyages en Scandinavie &c. pi. v. fig. 1, a-u. 1852. Cuma Rathhii, Lilljeborg, CEfversigt af Vet.-Akad. Forhandl. p. 6. 1856. Diastylis Rathhii, Bate, Ann. & Mag. Nat. Hist. 2nd ser. xvn. p. 451, pi. xiii. 1859. Diastylis Rathhii, Danielssen, Beretning om en Zoologisk Reise foretag. Som. 1857, p. 7. 1864. Diastylis Rathhii, G. O. Sars, Om Cumacea, Chr. Vid.-Selskab. Forhandl. 1864, p. 35, and 1873, Om Cumaceen fra de store dybder i Nordishafvet, Kongl. Vet.-Akad. llandl. Bd. ii. no. 6, p. 7, pi. iii. figs. 8, 9. 'Lightning' Expedition, Station 3, lat. 60° 31' N., long. 9° 18' W., 229 fathoms. l Valorous ' Expedition, Station 4, Davis Strait, lat. 66° 59' N., long. 55° 27' W., 60 fathoms. This polar species is widely distributed in the Arctic and Boreal North Atlantic. I have seen it from Greenland, river St. Lawrence, N.E. America (New-England coast), Norway, Sweden, and Great Britain. Professor G. O. Sars has, I think, fallen into error* in supposing that Cuma angulata of Kroyer is the male of his C. Rathhii. Both sexes of D. Rathhii are alike in the spiny armament of the carapace, consisting of two longitudinal lines of spines, one on each side of the dorsal line ; these spines are largest and widest apart just behind the rostrum, where the spines are also usually in pairs on each line ; the two lines gradually converge backwards, the spines rapidly decreasing in size, so as entirely to disappear at some distance from the hinder margin of the carapace. Among a collection of N.E. American Cumacea, for which I am indebted to Mr. L. I. Smith, is a Diastylis which I take to be the true Cuma angu-lata of Kroyer. * Beskrivelse af de paa Fregatten Josephines expedition fundne Cumaceer, 1871, pp. 5 and 21.
BioStor
