40 THE VOYAGE OF H.M.S. CHALLENGER. 



Sycon raphanus, 0. Schmidt. 



Sycon raphanus, 0. Schmidt, Spong. d. adriatisch. Meeres, Bd. i. p. 14, 1862. 

 Sycandra raphanus, Hreckel, Kalkschwamme, Bd. ii. p. 312. 



There are amongst the Challenger SyconicUe two specimens which I determine as 

 Sycon raphanus, var. tergestinum, H., their skeleton presenting no difference from 

 that of the variety just named, and the chief specific character of Sycon raphanus, 

 i.e., the slenderness of the subgastric triradiate spicules in comparison with other 

 spicules of the skeleton, being expressed very clearly. Most of these slender spicules 

 are clearly triradiate, some of them are provided with a short apical ray, rarely 

 exceeding 0"05 mm. in length. This is, however, no special character of the Challenger 

 specimens ; I have also observed it in those from the Adriatic, and think it to be 

 common to the whole species. Both the specimens proved to be full of Amphiblastulse. 



Coloxir. — Pale yellowish. 



Habitat. — Station 135, October 16, 1873. Island of Tristan da Cunha. Depth, 60 to 

 90 fathoms; rock, shells. Station 209, January 22, 1875 ; lat. 10° 10' N., long. 123° 

 55' E. ; Philippine Islands ; depth, 95 to 100 fathoms ; mud. 



Sycon arcticum, Hseckel, sp. (PI. III. fig. 5). 



Sycandra arctica, Haaekel, Kalkschwamme, Bd. ii. p. 353. 



Sycon arcticum can be easily distinguished from all other species of the genus by the 

 equal size of its tubar, gastric, and subgastric spicules, by their slenderness, and by the 

 circumstance that most of the tubar spicules are not triradiate but quadriradiate, with a 

 more or less developed apical ray. 



There is also, according to Hseckel, another more important distinction, viz., the 

 absence of the intercanals ; but we have already seen that this is erroneous. The inter- 

 canals are in Sycon arcticum, as in every Sycon, in their usual places, and their course 

 is represented on PI. III. fig. 5. Both the Challenger specimens of the species, one from 

 the Philippine Islands, the other from the Bermuda Islands, must be determined as 

 var. maximum, H. I did not find any generative elements in the former; but, on the 

 contrary, the specimen from the Bermuda Islands proved to be full of larvae (Amphi- 

 blastulse) and spermospores. 



Sycon arcticum has hitherto been considered to be an exclusively arctic sponge ; its 

 distribution must now be extended southwards, but it is to be noticed that while its 

 arctic forms belong to the largest of the Syconidse, their body reaching 50 mm. in length 



