90 0,^ THE VOYAGE OF H.M.S. CHALLENGER. 



^^ Stephanactis ahyssicola (PI. II. fig. 13). 



Actinia ahyssicola, Moseley, Trans. Linn. Soc, ser. ii., Zool., vol. i. p. 29", [)1. xlv. fig. 5. 



Both parts of the wall smooth ; cii'cular swelling distinctly defined ; tentacles in 

 two alternating circles. 



Habitat.— Station 46. May 6, 1873. Lat. 40° \T K, long. GG° 48' W. Depth, 

 1350 fathoms. Two specimens. 



Dimensions. — Length, 3*5 cm. ; height, 0'5 cm. 



Colour. — (Determined by Moseley in the fresh condition), the part inside the circular 

 swelling a beautiful rose-red with a few darker radial streaks ; the remainder of the wall 

 reddish-yellow and paler, especially the circular swelling ; oral disk rose-red with paler 

 tentacles. 



Of the two specimens of Stephanaclis ahyssicola, one was so much destroyed as to be 

 of no use for anatomical examination, and I did not wish to cut up the other as it was the 

 only well-preserved specimen of the species. Stephanactis ahyssicola is clearly so closely 

 allied to Stephanactis tuherculata that t deem a more detailed anatomical study 

 unnecessary, and therefore confine myself to the description of its external appearance. 



The body is elongated like that of Stephanactis tuherculata, but not prolonged into a 

 process at either end. The pedal disk enclosed the stem of a Mopsea so completely that 

 its margins were firmly joined on the lower side. The line of union is slightly undulated, 

 and the insertions of from ninety to one hundred septa, which lie more closely compacted 

 at the two ends of the body, shine through beside it. The spaces between the septa 

 are larger towards the broad sides, but become narrower again towards the middle of the 

 broad sides. 



The circular swelling, which Moseley erroneously terms the muscular swelling, is, 

 however, distinctly defined on either side. A small depression, in which rises a j^apiUa, 

 lies on either side close under the circular swelling in the middle of the broad side, 

 resembling those which we have met with in the same position, but in larger number, in 

 Stephanactis tuherculata. Otherwise, the wall is smooth, both in the portion lying 

 inside the circular furrow and that lying outside. It is incompletely contracted, so that 

 the oral disk, the oral opening, and part of the points of the tentacles are visible. As 

 the oesophageal grooves plainly occupy the middle between the two ends of the oval oral 

 fissure, it may be again safely assumed that the elongation of the body has taken place in 

 the direction of the transverse axis. Numerous small tentacles (sixty according to 

 Moseley) lie in a double row on the margin of the oral disk. 



Stephanactis ahyssicola is distinguished from Stephanactis tuherculata by its smaller 

 size, by the absence of knobs on the upper part of the wall, and by the lesser number of 

 cinclidal papillas. These are all differences, however, which may possibly arise from 

 difierence of age, and it is quite likely that the two species might require to be united, if 



