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



body ovate, short, and about twice as long as broad. The mouth is terminal, slightly 

 turned towards the ventral surface. The anus is large, of an almost triangular form. Only 

 five tentacles are left, but traces are seen of five others which have been torn off ; some of 

 those of the ventral surface seem to be a little smaller. The tentacles are very hard, 

 brittle, and non-retractile ; their ends are rather large, bearing round the edge small re- 

 tractile processes, the form and length of which are unknown. In consequence of their 

 brittleness several pedicels are broken, but from the traces left on the body-wall they seem 

 to be eighteen in number, nine along each side of the ventral surface. As the first pair 

 is situated almost 20 mm. behind the tentacles, the anterior part of the body is destitute 

 of pedicels. This first pair is comparatively the largest, about 9 or 10 mm. in length, 

 and the others diminish gradually backwards, the hindmost ones being very small. The 

 ends of the pedicels are slightly enlarged. As the processes on the dorsal surface are 

 torn off, it is impossible to state their length and appearance, but the large holes in the 

 body-wall indicate clearly that they must have been of great size and four in number. 

 They project from the anterior part of the back and are arranged in paii-s of which the 

 first one is a little closer to the middle line of the back than the others. The integument, 

 especially on the back, is of an unusual solidity and brittleness, in consequence of the 

 presence of numerous crowded pyramidal papillae (PI. XXXIX. fig. 2), which are larger 

 and visible to the naked eye on the back, but towards the ventral surface are almost 

 indistinguishable. Each papilla contains a calcareous deposit (PL XXXIV. fig. 3) com- 

 posed of four, up to 0"6 mm. long, spinose, arcuate arms, following the four edges of 

 the papilla towards its base, and one or two "rather long, straight, spinose processes 

 directed outwards from the body ; these processes run out from the centre of the 

 deposit, that is to say, almost from the top of the papilla, where the arms are joined 

 together. The integument is therefore rather rough. As the papillse are largest 

 and most distinct on the back, so the calcareous deposits also are largest there, their 

 arms being more distinctly curved and directed inwards than is the case with those of 

 the ventral surface. The pedicels as well as the tentacles are furnished with a great 

 number of deposits, resembling those of the ventral surface of the body, but commonly 

 a little smaller and with the arms more irregularly curved. Besides, several other 

 kinds of deposits (PL XXXIV. fig. 4) are to be found, especially in the pedicels, viz., 

 four-armed ones with the arms either unusually long and curved or short and straight ; 

 and smaller or larger, unbranched, straight or curved, more or less spinose spicula. 



The polian vesicle is 4 mm. long. The alimentary canal is of a brownish colour. 

 The cloaca is large and without any csecal prolongation. 



Elpidia rigida, n. sp. 



Body subovate, nearly twice as long as broad. Mouth anterior, ventral. Anus 

 posterior, subdorsal. Tentacles of apparently equal size, their terminal part bearing 



