192 DISCOVERY REPORTS 



The embryos vary from 0-5 to o-8 mm. in length. Some of the younger are of very 

 irregular shape where they have been tightly packed against their neighbours. In the 

 largest embryos the sucking disk and vestibulum are clearly marked; the oral plates 

 and the basal plates are nearly in contact with each other and one another. I cannot see 

 infrabasals ; there are about 20 stem-plates and a very large terminal plate. The basal 

 circle embraces the stem. I have seen bands of cilia around some of the embryos. 



Most of the distal pinnules are of the same number of segments and length as the 

 outer genital pinnules but they become shorter towards the end of the arm. (In small 

 specimens they are of 16-20 segments, 8-10 mm. long.) The first two segments are 

 short and stout with strongly spiny distal edges. The remainder, but for the last four 

 or five, are strongly compressed from side to side and gradually taper ; their distal edges 

 are beset with fine spines. The ambulacral furrow does not extend on to the last four 

 or five segments ; they are slender and rounded and strongly spiny. 



The disk appears to be naked in the few specimens in which parts of it can be seen, 

 the anal cone high. 



Sacculi are abundant and conspicuous, regularly arranged on the disk, the arms and 

 the pinnules ; in some of the specimens they have retained in spirit a beautiful red colour. 



Along the pinnule ambulacra of the small- and medium-sized specimens there are 

 heavy well-developed side-plates, about three pairs to each segment, but no cover-plates 

 (Fig. 18 /). Spicules occur in most of the tentacles; they may be simple smooth rods, 

 but are more often very thorny and are sometimes branched. The large specimen lacks 

 distal pinnules ; there are no side plates along its genital pinnules but there are abundant 

 spicules in its tentacles. 



Notes of the colour of five of the specimens were made at the time of capture. Four 

 of them were lighter in the proximal than the distal part. The proximal third to half 

 varied from straw-yellow to bright orange yellow ; the distal part from a delicate pink 

 to a deep orange brown. The fifth specimen was orange yellow. The specimens retain 

 yellow or pink tinges, deeper in the more distal part, in spirit. The basal segments of 

 the cirri are darker in colour than the rest. 



A series of pentacrinoid larvae of this species is described on pp. 202-210. 



This is by far the largest and most robust species of Isometra (Plate V). It is dis- 

 tinguished from all others by its longer cirri made up of more numerous segments. 

 From /. vivipara which most nearly approaches it in size, and from /. flavescens which 

 is smaller, it is further distinguished by differences in the proportional lengths of the 

 oral pinnules. 



