202 DISCOVERY REPORTS 



Large triangular oral plates are present near the mouth. 



The posterior interradius is damaged and too broken to show if the radianal plate 

 remains. 



Pentacrinoid larvae of Isometra hordea n.sp. 



There are fifteen pentacrinoid larvae from St. 170 (23. ii. 27. Off Cape Bowles, 

 Clarence Island, 61° 25' 30" S, 53° 46' W, 342 m.) which form a series. The youngest 

 is a prebrachial or cystid stage; the oldest has three whorls of cirri on the topmost 

 columnal of its stem, and arms of about thirty brachials. 



From the same station there are eighteen pentacrinoids of Notocrinus virilis which 

 are described hereafter (p. 210). 



The adult crinoids taken at this station were: 



Promachocrimis kerguelensis 6 



Isometra hordea 3 



Notocrinus virilis 17 



A'^. mortenseni 2 



It does not follow that the pentacrinoids of the present series belong to any one of 

 these species but it is probable that they do. I believe them to be Isometra hordea. They 

 are not of Promachocrimis kerguelensis, the stages of which are known (see above). They 

 do not closely resemble the pentacrinoids oi Notocrinus virilis as one would expect those 

 of A^. mortenseni to do. On the other hand, they do appear to show some resemblances 

 to Isometra hordea. 



The shapes and proportions of the primibrachs and brachials of the oldest larvae and 

 of /. hordea are similar. The distal brachials of the oldest pentacrinoid have a slight 

 zigzag character suggestive of that of the middle part of the arms of /. hordea. The 

 pinnule ambulacra are lined by side-plates and the tentacles have numerous spicules, 

 the former not unlike, the latter resembling, those of /. hordea. 



1. This is the only specimen of a cystid or prebrachial stage (Fig. 21 a). 



The crown is 0-9 mm. long. The column is of 26 segments and 3-4 mm. long. The 

 distal part of the column is narrower than the proximal. The first four or five columnals 

 are very short and discoidal, much shorter than wide, but increasing in length. The 

 middle columnals are nearly as long as wide, the distal are slightly longer. All are con- 

 siderably wider medianly, where they are encircled by a narrow girdle, than at either end ; 

 they are evenly rounded off towards each end. The terminal plate is thick and rounded. 



The base of the basal cup is considerably wider than the topmost columnals. The sides 

 are faintly convex. The height of the cup is about two-thirds of the distal width. The 

 orals form a cup slightly higher than the basals. The lateral edges of the orals are strongly 

 bent outwards to give a high double ridge along each of the sutures between them. 

 When the crown is seen with these ridges in profile the oral cup has more strongly 

 convex sides than the basal. 



2. In this stage the five radials and the radianal plate are present (Fig. 21 b). The 

 crown is about i mm. long, the column 5-8 mm. 



