I40 DISCOVERY REPORTS 



the same length as Pj, but sometimes, when it is a genital, it is very much shorter 

 and of segments which diminish rapidly in stoutness from the base to the end. P3 is 

 usually of anything from 5 to 20 fewer segments than P2 of the same specimen ; all but 

 its basal segments are more elongated, being as much as, or more than, twice as long as 

 broad. 



The middle genital pinnules are of about 20-26, exceptionally more, segments ; they 

 are 10-20 mm. long, sometimes considerably longer. The outer pinnules are of about 

 the same length or longer. In both the genital and outer pinnules the first segment is 

 very short, the second longer but not so long as broad, the others considerably longer 

 than broad. 



The way in which the primary ambulacral furrows on the disk divide so as to provide 

 the arms is very variable though certain arrangements appear to be more constant than 

 others (see below). 



Sacculi are abundant on the pinnules. 



Along the sides of the pinnule ambulacra there may be a single continuous series of 

 large plates, three or four to each pinnule, the distal edge of one overlapping the 

 proximal of the next. Each is curved in the axis of the pinnule and has its outer part 

 curved over the ambulacral furrow. Clark (1921, p. 268, fig. 378) has described them 

 at their highest development. When they are present the tentacles contain numerous 

 knobbed spicules. The plates may be smaller, and therefore not touching one another, 

 or very much smaller and fewer: in some specimens the pinnules have only one or two 

 extremely simple small plates near the end (Fig. 2 c). They are often entirely absent. In 

 some specimens with reduced plates the spicules are few ; if the plates are very reduced 

 they may be absent : this is so in over twenty-five specimens of the present collection. On 

 the other hand, it is only in one specimen that there are spicules (and they are few) and 

 no plates. (It was, of course, only three or four pinnules of any specimen that were 

 examined.) The presence of plates and spicules has been regarded as a sign of im- 

 maturity. The examination of the present collection has shown that it is not so, but that 

 there does appear to be some correlation between the degree of development of the plates 

 and spicules in a number of specimens and the locality in which they occur (see below). 

 The colour is very variable. The entire specimen may be straw-coloured, very light 

 grey, flesh-coloured, pale or brilliant yellow, orange, brown or purple; the greater part 

 of it may lack stronger colours except for bands of dark brown or purple on the cirri, 

 or the arms (when the bands often coincide with the syzygial pairs), or the pinnules, or 

 all three ; or portions of a specimen, such as the pinnules or the distal parts of the arms, 

 may be brown or purple or yellow. There may be great variation in the colour of the 

 specimens of one colony as is shown by a note, made at the time of capture, describing 

 the eight specimens from St. 42 : " The animals showed a gradation of depth of colouring 

 ranging from cream to very light grey or flesh, to pale or deep chocolate brown, to dark 

 purple. The colour was usually least developed on the cirri, and— grading through the 

 arms — most enforced on the pinnules; it was sometimes equally developed on all." The 

 gonads were bright orange. 



