194 PERCY SLADEN TRUST EXPEDITION 



to the perradial tentacles, and eight adjacent to the interradial cirri. Bigelow (1909) 

 could only find eight sense organs in specimens collected in the Eastern Pacific. 



There should be no diflficultj in seeing sense organs in living specimens, but after 

 specimens have been preserved for some time the sense organs frequently have a 

 marvellous way of either disappearing or so changing their appearance that it is not an 

 easy matter to recognise them. Among the specimens in the " Sealark " collection 

 I have found three with sense organs adjacent to the peri-adial tentacle and in one of 

 the specimens the root of the adradial cirrus was visible. The tentacles and cirri are 

 broken oflP in most of the specimens. When any are present it is the interradial cirrus. 

 Only about three specimens have any perradial tentacles left and the adradial cirri have 

 either not developed or else broken oflf at the base. 



Hhopalonema velatum is widely distributed throughout the warm regions of all the 

 oceans. It is generally found at or near the surface. 



Bigelow (1909) after an examination of a large series of specimens collected by the 

 "Albatross " in the Eastern Tropical Pacific, has come to the conclusion that Rhopalonema 

 velatum, Gegenbaur, and Rhopaloneina cceruleum, Haeckel, are identical. In 1906, when 

 I reported upon specimens of Wiopalonema cceruleum collected in the Bay of Biscay, 

 I certainly felt sure that Rhopalonema velatum, and Rhopalonem,a cceruleum. were 

 distinct species. The distinguishing character was based upon the shape of the gonads, 

 which in Rhopalonema velatum are either globular or oval, but in the Biscayan 

 Rhopalonema cceruleum the gonads form narrow bands, which occupy the central 

 third of the radial canals. Although I have re-examined the Biscayan specimens, still 

 I am not yet convinced that they are identical with Rhopalonema velatum. 



Mayer (1910, p. 380) regards Rhopalonema cceruleum, Haeckel, as a distinct and 

 good species. Under its name he has placed the following : — Rhopalonema cceruleum,, 

 Maas (1905) ; Browne (1906). Rhopalonema funerarium, Vanhoffen (1902) ; Bigelow 

 (1909). Bigelow considers the Rhopalonema cceruleum, Haeckel and Browne, to be 

 identical with Rhopalonema velatum, Gegenbaur. Mayer, on the other hand, regards 

 it as identical with Rhopalonema funerarium,. I cannot agree with Mayer's synonymy, 

 for, I believe, that he has mixed up two distinct species; Rhopalonema cceruleum,, Haeckel 

 and Browne, belongs to one species, and Rhopalonema funerarium, Vanhoffen (1902), 

 Bigelow (1909); Rhopalonema cceruleum, Maas (1905) belong to another species. 



30. Sminthea eurygaster, Gegenbaur, 1856. 



Sminthea eurygaster, Gegenbaur, 1856, p. 245, Taf. 9, figs. 14 — 15. 



Trachynema eurygaster, Haeckel, 1879, p. 260. 



Trachynema mammceforme, Haeckel, 1879, p. 262, Taf. 17, figs. 13—15. 



Sminthea eurygaster, Metschnikoflf, 1886, p. 244, Taf. 1, figs. 18—20. 



Trachynema eurygaster, Maas, 1893, p. 12. 



Trachynema eurygaster, Browne, 1906, p. 171. 



Sminthea eurygaster, Mayer, 1910, p. 383, text-figs. 226—227. 



Localities. North of Chagos, Lat. 4° 16' S., Long. 71° 53' E. 125—0 fms. 17 May, 

 1905, B. 1 specimen. 50 — fms. 18 May, 1905, F. 2 specimens. Chagos Archipelago, 



