172 ME. E. T. BROWNE — BISCATAN PLANKTON : • 



CoLOBONEMA SERICEUM, Vanlioffen, 1902, ID. 56, Taf. 9, 12. 



There is one specimen. The umbrella, owing to the firmness of the jelly, has retained 

 its shape very well, hut the preservation is by no means good. 



The umbrella is highly curved, about 18 mm. in height and in width ; the velum is 

 broad, about 4 mm. The stomach is very short ; it is contracted, and forms simply a 

 narrow ring about 2 mm. in diameter. Eight radial canals. There are indications of 

 gonads extending along the radial canals, as figured by Yanhoffen, but the canals are in 

 a macerated condition, and nearly all the circular muscles on the sub-umbrella have 

 disappeared. There are 32 tentacles, all of which are broken off close to the base. The 

 per-canal (opposite the radial canals) and ad-canal tentacles are very mvich larger than 

 the inter-canal tentacles; the latter are just beginning to develop. The root of a 

 tentacle resembles Vanhoffen's figure (Taf. 12. fig. 42). Sense-organs were searched for, 

 but were not found. 



Occurrence : 250 to fathoms. 36 h (1 specimen). 



lihtribution. — This species is one of the new deep-sea medusae discovered by the 

 ' Valdivia.' It was found off the west coast of Africa from the Gulf of Guinea to the 

 south of Cape of Good Ilope (lat. 42° S.), and also widely distributed over the Indian 

 Ocean. It was taken in open vertical nets worked from the depth of about 1600 to 

 650 fms., once in a closing-net working between 820 to 500 fms., and once in a trawl at 

 about 350 fms. Its occu.rreDce in the Bay of Biscay considerably extends the area of 

 its distribution. 



I have associated the Biscayan specimen with Vanhoffen's sjiecies because the latter 

 was also found in the Atlantic. Maas, however, has described a Colobonema { C. typicimi ?) 

 found by the 'Siboga' Expedition in the East Indies (Straits of Makassar; off Timor, 

 Ceram, and other islands), and taken at a depth of about 1350 to 230 fms. He suggests 

 that it is probably identical with Colobonema sericeum and with Somceonema typlcimi, 

 Maas, 1897. This latter species was found in the Pacific, off Costa Rica, and in the 

 Gulf of California. I think that the specimens of Colobonema collected on the 'Valdivia' 

 and ' Siboga ' Expeditions probably belong to the same species, but am rather doubtful 

 about their connection with Somceonema typicum. 



Rhopalonema ccertjleum, Haeckel, 1879, p. 264, Taf. 17. figs. 3-6. 



There are about seventy specimens, but out of these only about a dozen are in fairly 

 good condition. Many have the margin of the umbrella in such a bad state that the 

 tentacles, cirri, and sense-organs have completely disapj)eared. 



Description based upon the largest Sp)ecimens. — The umbrella is fairly higlily curved, 

 with a small somewhat conical top-knot. There is a slight variation in the shape of the 

 umbrella and in the shape of the top -knot. The figure by Haeckel (Taf. 17. fig. 3) 

 gives a fairly good idea of the shape of the umbrella, but most of the Biscayan specimens 

 have a slightly more rounded umbrella. The umbrella is broader than high. Among 

 the larger specimens the height remains fairly constant, about 6 to 7 mm. The width 

 is variable, 7 to 10 mm. The ex-umbrella is marked with radial furrows, which may be 



