200 DISCOVERY REPORTS 



Isometra hordea and Notocrinus virilis. In describing them I have followed A. H. Clark 

 in calling the plate in the posterior interradius the radianal plate : it is the anal plate of 

 other authors. 



Mortensen (1920, p. 74) says that it appears to be a general rule among comatulids 

 that: the anal (radianal) plate develops in the radial midline like the true radials but 

 before any of them ; the right posterior radial is the last of the radials to develop ; it 

 appears to the right of the anal plate and outside the radial midline, and only later, 

 during growth, assumes the radial position by pushing the anal plate to the left. 



Clark has described a long series of Promachocriniis kerguelensis pentacrinoids con- 

 taining specimens much younger than mine. There is not in my series oi Isometra hordea 

 and Notocrinus virilis any specimen with the radianal plate but with no right posterior 

 radial. Nevertheless the younger stages of Isometra hordea do appear to confirm 

 Mortensen's general rules. 



In specimen No. 2 of Isometra hordea all the radials are present, but the right posterior 

 is smaller than the others ; in No. 3 each of the radials except the right posterior carries 

 a costal and an axillary (Fig. 2\b,c). These conditions probably arose because the right 

 posterior radial was the last to appear. No. 2 shows too that the radianal appears first in the 

 radial midline, the posterior radial to the right of and slightly above it. In some of the 

 stages which follow (Nos. 3 and 5-7) the suture between the posterior and right posterior 

 orals— which is the axis of the right posterior ray— lies to the right of the suture between 

 the corresponding basal plates. This, it is probable, is because the right posterior radial 

 of each first appeared to the right of the radial midline ; it comes to occupy the true radial 



position later. 



Similarly, in three of the younger pentacrinoids of Notocrinus virilis (Nos. 3, 6 and 7) 

 the axis of the right posterior ray lies to the right of that of the suture between the 

 posterior and right posterior basals. 



Pentacrinoid larvae of Promachocrinus kerguelensis Carpenter 



A. H. Clark (1921, pp. 530-57, figs. 881-937) has described a series of forty-three 

 pentacrinoids of Promachocrinus kerguelensis, the youngest without any radial structures, 

 the oldest with large and prominent interradial plates and three whorls of cirri on the 



proximal columnal. 



There is in the present collection a pentacrinoid from South Georgia (St. 27, i lom.) 

 with interradial structures which is certainly P. kerguelensis; there are two younger 

 pentacrinoids, one from the South Sandwich Islands the other from the Bransfield 

 Strait region, which I believe to belong to this species. All three were taken in 



March. 



No other crinoid but P. kerguelensis is known from the South Sandwich Islands, 

 though others may well occur. The pentacrinoid from there (St. 366, 77-152 m.) is 

 the youngest of the three. It resembles Clark's No. 33 (pp. 546-7> %§. 922-3). The 

 crown is 1-3 mm. long. The stem is incomplete, of 23 columnals, the longest of which 



