4i 



There are thus tvvo forms, albida and sibogce, which may be definitely regarded as representatives 

 of the genus Arachnactis, and two others, brachiolata and bournei, which should be removed 

 from that genus. What the systematic position of the latter two may be it is a little difficult 

 to say. Van Beneden (1898) has assigned A. bournei to C. lloydii, principally on the basis 

 that the areas of distribution of the two forms is essentially the same, and if this identification 

 be correct, it may be expected that it will be found that the second couple of protocnemes of 

 bournei actually do become the telocnemes. Similarly Kingsley (1904), with an equal amount 

 of probability, has regarded brachiolata as the larval form of C. vcrrillii, and if both these 

 identifications prove correct the two larval forms must be associated with the Dianthca nobilis 

 of Busch (1851), which is generally accepted as the larval form of C. membranacea. 



8. Arachnactis sibogcc n. sp. 



Stat. 96. South-east side of Pearl Bank, Sulu Archipelago. Plankton. 1 ex. 



Stat. 205. Lohio Bay, Buton Strait. 3 ex. 



Stat. 282. Between Nusa-Besi and the north-east point of Timor Island. 1 ex. 



In the majority of the specimens which may be referred to this species the body is short 

 and almost spherical, but in an individual from Station 205 (PI. I, fig. 10) it is more elongated 

 and conical, this individual, however, notwithstanding its greater size and difference of form 

 being in practically the same stage of development as the others. The marginal tentacles in 

 all were nine or ten in number, four on each side of the median plane being long and slender, 

 while a median one was much smaller; four or five labial tentacles were present (PI. I, figs. 9 

 and 10). The individual from Station 96 cliffered from the rest in being much smaller and the 

 marginal tentacles, while considerably longer than the breadth of the disc, lacked the almost 

 disproportionate length which they possess in the other examples. 



Dimensions. - In the example from Station 96 the diameter of the column was 

 0.6 mm. and the length of the longer tentacles was 1.5 mm. In the other spherical examples 

 the diameter of the column was 0.75 mm. and the longer marginal tentacles reached a length 

 of 3.5 mm. The conical example from Station 205 had a length of about 1.5 mm., and the 

 diameter at the margin was 0.6 mm. ; owing to their contorted form the length of the marginal 

 tentacles could not be determined accurately, but they seemed to be relatively shorter than 

 those of the other examples from the same Station. 



Colouration. — All the specimens were completely colourless, the only indication of 

 a possible presence of pigment being a distinct opacity at the tips of the marginal tentacles. 



Structure. - The arrangement of the mesenteries is shown in the adjoining, text-figure 

 (Text-fig. XII) prepared from one of the spherical examples from Station 205. In this there 

 were four couples of well developed marginal tentacles, a small median tentacle and on the 

 right side an additional tentacle whose fellow had not yet made its appearance. The labial 

 tentacles were five in number, two couples corresponding to the second and third couples of 

 marginal tentacles, while the odd one was one of an additional couple, developed, like the odd 

 marginal, upon the right sicle. 



The mesenteries were twelve in number, equally distributed on each side of the median 



SIBOGA-EXPEDITIE XV cl. 6 



