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



carries round lobes, the number of which is similar to that of the spokes. The large wheels 

 are most numerous in the walls of the processes and in the dorsal perisoma, and are on the 

 contrary very scattered on the ventral surface and in the pedicels and tentacles. Those 

 large wheels of the individuals dredged at Station 169 are provided with up to fifteen 

 spokes, and with a crown constructed of from five to six arms ; instead of the large hole 

 in the centre of the nave, there are frequently found several very small ones, in which 

 case the centre of the nave is joined to the top of the crown by a short minute rod 

 (PL XXXII. fig. 6). The small wheel-shaped plates (PI. XXXII. fig. 5), about 0-052 mm. 

 in diameter, are slightly convex and perforated by about fifteen holes, of which the four 

 central ones are larger than the others which surround them ; these plates, which are 

 sometimes provided with five central holes, are found everywhere in the perisoma. 



The processes and pedicels contain, besides the above-mentioned forms of deposits, 

 partly larger, scattered round plates (PL XXXII. figs. 7) which measure about - 072 mm. 

 in diameter, and are supplied with from thirty-five to fifty holes, partly a few straight or 

 arcuated simple or branched spinose spicula (PL XXXII. fig. 9) ; in addition, one or more 

 large plates of a more irregular form are distinguishable at the top of the processes 

 (PL XXXII. fig. 8). The terminal part of the pedicels is strengthened by several layers 

 of calcareous bodies, the innermost of which is most developed and made up of plates 

 (PL XXXII. figs. 11, 12) perforated by numerous round holes, which decrease in size 

 towards the uneven circumference ; outside those lie fragde and net-Hke bodies with 

 wide irregular meshes. The oral-disk is provided with numerous simple, more or less 

 straight and spinose spicula, with the ends sometimes bipartite. The calcareous ring 

 is rudimentary, fragile, and spongy; it has not been possible to distinguish its true form 

 and structure. 



The polian vesicle, large and wide, measures about 27 mm. in length. The niad- 

 reporic canal seems to communicate with the exterior by several pores, though from want 

 of material I do not feel convinced about it ; its walls contain a thin thread-like 

 calcareous network (PL XXXII. fig. 13). The pedicels are in connection with elongated 

 ambulacral cavities within the perisoma, whde the processes communicate with small 

 branched vesicles hanging into the peritoneal cavity. The reproductive organ is com- 

 posed of two large fascicles about 60 mm. in length, which are situated one on each side 

 of the medio-dorsal mesentery ; each fascicle is made up of several bundles of dicho- 

 tomously branched, elongated, caecal sacks. The genital aperture is situated about 

 30 mm. behind the tentacles. 



Family III. Psychropotid^. 



Body more or less elongated, either subcylindrical and vermiform, or very flat and 

 depressed, or rather high posteriorly and decreasing gradually forwards ; its anterior part 



