Leucon longirostris G. O. Sars

Calman, W. T., 1921, Leucon longirostris G. O. Sars in The Cumacea of the Puritan Expedition, Mittheilungen aus der Zoologischen Station zu Neapel 17, pp. 414-416 : 414-416

Leucon longirostris G. O. Sars

(Pl. 27, figs. 1-8) .

L. longirostris, G. O. Sars , Svenska Vet. Akad. Handl. 9. Bd. 1871 No. 13 p. 42 fig. 75. Norman, Ann. Mag. N. H. (5) Vol. 3 1879 p. 69.

Description of sub-adult female ( fig. 1 ). Total length 5.7 mm.

Carapace (including; pseudo-rostrum) about 31/ 2 times in total length, the dorsal crest horizontal posteriorly, strongly curved downwards in front and armed in its anterior two-thirds with about seven stout curved teeth, well separated and diminishing in size posteriorly. Pseudo rostrum ( fig. 2 ) more than i / 3 of total length of carapace, straight, tapering to an acute point and directed slightly upwards. The lower margin bears two or three more or less distinct teeth near the base. Antero-lateral margin nearly straight with a narrow but deep antennal notch above w T hich bears three or four stout teeth. Antero-lateral angle not produced but bearing a strong tooth, followed by a series of successively diminishing teeth on the lower margin. The pleural plate of the penultimate thoracic somite is produced into a sharp curved tooth posteriorly, and there is a pair of curved teeth 011 the sternal surface of the last thoracic somite (not one as stated by Norman) a little in front of the insertion of the last pair of legs ( fig. 3 ). The abdomen is about equal in length to the cephalothoracic region.

The antennules ( fig. 4 ) have the outer flagellum composed of three segments, the first equal in length to the last segment of the peduncle and the terminal one very small. The inner flagellum is unsegmented and is equal in length to the first segment of the outer. It bears several long and rather stout setæ at the tip.

There is a row of strong teeth on the lower surface of the basis of the first legs. Uropods ( fig. 5 ) a little shorter than the last two somites together, the peduncle longer by one quarter than the last somite, carrying about five spines on its inner edge. Endopod one-third longer than the peduncle, the proximal segment more than three times as long as the distal. Fifteen spines 011 inner edge of proximal and five on distal segment besides the stout terminal spine. One long and several short seta; on outer margin. Exopod a little longer than first segment of endopod, bearing setæ on both margins and a group on the apex.

Adult male ( fig. 6 ). Total length 6,0 mm. Carapace 1/ 4 of total length, the dorsal crest unarmed. Pseudorostrum ( fig. 7 ) 1/5 of total length of carapace, horizontal and obliquely truncate. The lower angle bears one or two teeth. Antero-lateral margin straight and vertical, without antennal notch, with two teeth above near base of pseudorostrum. Tooth on antero-lateral angle followed by a series of serrations on anterior part of lower margin.

The pleural plate of the penultimate thoracic somite is not

W. T. Caiman produced posteriorly, but the sternal surface of tlie last somite bears two curved teeth as in the female. The outer flagellum of the antennules is composed of four segments. As in the female the inner flagellimi is equal in length to the first segment of the outer.

Uropods ( fig. 8 ) considerably longer than the last two somites together, peduncle about one-third longer than the last somite with about nine long spines and setæ on its inner edge. Endopod nearly one-half longer than peduncle, the proximal segment four times as long as the distal. There are very numerous spines of varying length on the inner edge and a few on the outer edge. Exopod not quite as long as the first segment of endopod.

Remarks. - This species was described by Sars from a fragmentary and immature male specimen. Norman added some details from a female specimen, probably also immature. The females and young in the present collection resemble closely Sars’ very characteristic figure and some of the specimens sent to me bore labels in Prof. Sars’ handwriting. There can, therefore, be no question as to the identification, although Sars’ description of the inner ramus of the antennule as " rudimentær og knudeformig" is at variance with the characters of the specimens examined by me.

Occurrence. - Stations 17, 18, 26, 30, 39, 44, 57. Depth 950-1200 metres.

Distribution. - Off coast of Portugal, 550 fathoms (Sars ; at entrance of Davis Straits, 1750 fathoms (Norman). 1