I 12 



Length of the males about 15 mm., of the ovigerous females 15.5 — 21 mm. 



Young Specimens (figs. \i — 4«/). — Figs. 4/ and \k represent the anterior part 

 of a young female, measuring 10.5 mm. in length, respectively from above and from the side; 

 in the same way figs. 4/ and 4^ represent a much younger specimen measuring only 7.2 mm. 

 These figures, as compared with each other and with figs, a, a and \b representing adult 

 specimens, show the reduction according to age of the frontal plate with rostrum, the development 

 of the eyes and the small keel containing the dorsal organ (the latter only visible under high 

 magnifying power). As in X. luicrops the frontal plate is extremely large in very small specimens, 

 and during the growth of the animal the plate alters its shape and becomes proportionately 

 much reduced in length. In the specimen measuring 10.5 mm. the upper section of the eyes is 

 distinctly larger than the lower (fig. 4/^), but the inner dark-coloured portion is lighter and 

 scarcely larger in the upper than in the lower section. In the very small specimen the whole 

 cornea is smaller in proportion to the stalk (fig. 4;//), the upper section is not very well defined 

 and a little smaller than the lower, while its darker inner part is very much smaller than that 

 in the lower section. The dorsal carina is much lower and le.ss pronounced than in young- 

 specimens in the same stage of development of X. luicrops. In these young specimens marginal 

 denticles on the carapace are distinct or even conspicuous. 



Remarks. — The specimen in the British Museum marked "type" by Sars was taken 

 South of the Cape of Good Hope; it measures 9 mm. and is a young of the present species. 

 In the adult males from the Atlantic the carapace has a pair of minute denticle on the lower 

 margin rather near the po.sterior end, but the copulatory organs are similar in specimens from 

 the North Atlantic and from the area explored by the "Siboga". 



Distribution. — I have specimens both from the subtropical part of the North 

 Atlantic and from the Pacific. 



Nematobrachion Caiman. 



This genus comprises 2 species, X. boopis Calm, and X. flexipes Ortm., both established 

 on specimens from the Atlantic. The "Siboga"' captured some specimens of the first-named species. 



18. Xematobrachion boopis Caiman. 



1896. Nematodactyliis boopis Caiman, Trans. Roy. Irish Acad. Vol. XXXI, p. 17, figs. 19 — 28. 

 1905. Nematobrachion boopis Caiman, Rep. Sea and Inland Fisheries of Ireland, 1902 — 1903, 

 Part II, App. 4, p. 153; PI. XXVI. 



Stat. 128. July 22. Lat. 4°27'N., long. 125°25'.7E. 1645 m. Hensen vertical net, from 700 m. 



to surface. 2 specimens (i immature and i very young). 

 Stat. 203. September 19. Lat. 3°32'.5 S., long. 124° 15'. 5 E. Hensen vertical net, from 1500 m. 



to surface. 5 specimens (i adult 9> ~ immature and 2 very young specimens). 

 Stat. 230. November 14. Lat. 3°58'S., long. i28°2o'E. HENSEN vertical net, from 2000 m. 



to surface, i young specimen. 

 Stat. 276. January 9. Lat. 6°47'.5 S., long. I28°40'.5 E. HENSEN vertical net, from 750 m. to 



surface, i immature specimen. 



