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



Stephanactis tuberculata, n. sp. (PI. III. fig. 7). 



Upper part of the wall covered with larger and smaller knobs, thickly compacted 

 together, lower part smooth ; tentacles in four to five alternating rows. 



Habitat.— Station 232. May 12, 1875. Lat. 35° 11' N., long. 139° 28' E. Depth, 

 345 fathoms. One specimen. 



Dimensions. — Height, 2 cm. Length of the pedal disk, 10 cm. ; length of the oral 

 disk, 3 "5 cm. ; breadth of the oral disk, 2 cm. 



The single specimen of Stephanactis tuberculata, which I was able to examine, is 

 attached to the axis of a Virgularia, from which the soft cortical layer has been com- 

 pletely stripped as far as the Actinia extends ; the pedal disk encloses the axis so com- 

 pletely that the two margins are pressed together, without, however, becoming fused, and 

 so form a sheath about 10 cm. long. The wall first runs about 2 cm. close to the pedal 

 disk, it then forms a body about 2 cm. high, which, being in a contracted condition, 

 becomes much smaller at the upper end ; the body appears fusiform when seen from the 

 oral side (fig. 7, a). 



A thick circular swelling, running near the upper margin, divides the wall into a smaller 

 upper and a larger lower portion. The former is slightly inverted as in the genus Phellia, 

 and may be completely overlooked from the outside. It is covered with numerous knobs, 

 which lie thickly compacted, smaller and larger intermixed. The smaller are usually 

 rounded spheroidally, whilst the larger stand out as nose-like projections above the level 

 of the smaller ; they may be divided into two by shallow furrows. 



The lower section of the wall is essentially smooth, as the transverse and oblkpie 

 wrinkles and furrows are merely caused by contraction. A more pronounced groove 

 extends on either side in a longitudinal direction, downwards from the circular swelling 

 at an equal distance from the two ends of the body (fig. 7). Four small knobs, in the 

 upper surface of which I could make out a little depression with a magnifying glass, 

 lie at the bottom of each groove. As I proved by means of transverse sections, these 

 depressions are the openings of fine canals, which pierce the wall, and form communica- 

 tions between the surrounding medium and the directive intraseptal spaces which lie 

 opposite to them ; they may be fitly compared to the cinclides of the genus Calliactis. 



The circular muscle lies in the knobbed upper part of the wall, and extends downwards 

 as far as the circular swelling. It occupies nearly the entire thickness of the mesoderm, 

 which however it does not greatly increase ; in transverse section it is elongated, nearly of 

 ecuial breadth throughout, and is only reduced a little in size towards the lower end. The 

 bundles of fibrillse are very small, and distributed with tolerable regularity in the 

 fundamental substance, so that we can hardly observe any arrangement into larger or 

 smaller groups. 



Though the sphincter is tolerably strongly contracted, we can make a partial survey of 

 the oral disk. It bears more than a hundred tentacles, placed in from four to five 



