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



they are of an elongated conical form, and some of them are almost as long as the 

 greatest breadth of the body. The body-wall passes imperceptibly into the processes, 

 consequently it is rather difficult to state their exact size at the base. The pro- 

 cesses are straight, brittle, and easily broken off, and appear to possess an extremely 

 slight degree of flexibility. The tentacles (PL XLIII. fig. 3), the discoidal ends of 

 which carry about eight minute retractile processes, are, as in Deima validum, small and 

 capable of being withdrawn, thus rendering it impossible to discover any traces of them 

 externally. The anterior circular aperture, which opens into the oral cavity in which the 

 tentacles are enclosed, is surrounded in this species also by a circular disk encircled 

 by a single crown of minute papillae (PL XLIII. fig. 2). The integument, which is 

 extremely brittle and hard, is supported by larger or smaller plates (PL XXXI. figs. 

 10, 11), which are crowded together and cover one another entirely or with their edges 

 alone, so as to form a kind of external skeleton of remarkable firmness. Now and 

 then some very large plates measuring up to 5 mm. are found, especially on the 

 dorsal surface, round which are arranged some small plates, which mostly overlap the 

 former ones. The inner surface of each plate is almost flat, whfle the outer is more 

 or less convex and rises towards its middle into a large conical knob, which is most 

 distinct and most prominent on the plates which belong to the back and to the processes. 

 The inner surface of the plates is perforated by more regularly circular holes, and upon this 

 inner surface, which doubtless is first formed, a very fine irregular network has arisen, 

 thus giving the plates the form described. The tentacles contain only a small quantity 

 of deposits (PL XXXI. fig. 13) in the shape of small oblong perforated spinose plates and 

 spinose irregular spicula. The deposits of the dorsal processes resemble the plates in the 

 integument, though they are smaller and of a more irregular form ; I have not been 

 able to distinguish any spicula, though they may possibly be present in the tops of the 

 processes which, in consequence of their brittleness, have always been broken off. The 

 plates on the pedicels seem to be destitute of the characteristic knob, or sometimes 

 possess a slight one; transversely disposed spicula (PL XXXI. fig. 12) support the ends 

 of the pedicels, which show no traces of a terminal plate. 



The calcareous ring (PL XXXVII. fig. 3) resembles in structure that of Oneiroj)hanta; 

 five rather large radial pieces are distinguishable, each supplied with a furrow for the 

 passage of the ambulacral nerves and canals. From want of materials I have not been 

 able to make a more detailed examination concerning the number of the interradial pieces. 

 The sutures are not visible between the different pieces, and the entire ring seems to 

 form a continuous whole of an extremely spongy structure. The polian vesicle is short 

 and widens behind. The water- vascular system seems to bear the most striking resem- 

 blance to that of Deima validum and Oneirophanta. The cloaca is insignificant. 

 The reproductive organ (PL XLVI. fig. 8) consists of two fascicles, each composed 

 of six or seven elongated cylindrical unbranched caeca. These caeca are very hard 



