PENTACRINOID LARVAE 211 



That these twenty pentacrinoids from the Bransfield Strait region are of N. virilis 

 is shown by the fact that they all carry in superficial pits in the orals, and sometimes in 

 other adjacent ossicles, glandular sacs similar to those described from the posterior end 

 of the embryos by Mortensen (1920) who has described the eggs and embryos of the 

 species. One of the larvae (No. 7) occurred on a cirrus of an adult A^. virilis. The last 

 three of the series (Nos. 18-20) have small plates in the naked perisome which separates 

 the oral plates from the radials : the perisome of adult A^. virilis is strongly plated. The 

 oldest larva has along the arm ambulacra strong side- and cover-plates of the same 

 nature as those of N. virilis. 



The series is not so complete as that of Isometra hordea. There is no prebrachial stage : 

 the youngest larva has arms of two or three brachials. The oldest has only one whorl of 

 cirri on the topmost columnal of its stem; its arms are of nineteen brachials. 



The adult crinoids taken at St. 170 are shown on p. 202. Those at St. 175 were: 



Promachocrinus kerguelensis 3 



Phrixometra mitrix i 



Isometra vivipara I 



Notocrinus virilis 7 



I. Length of crown ca. 1-4 mm. (Fig. 23 a); length of column ca. 6-4 mm. 



The column is of 34 columnals and a thick roughly circular terminal plate which 

 appears to be simple: I cannot see any supplementary plates like those known in 

 the larva. The first seven columnals are short and discoidal. The most proximal is in 

 close contact with the basal plates. From the second to the seventh there is a gradual 

 decrease in width. The eighth is about one-third, the ninth about a half, as long as 

 broad ; the proximal half of each is encircled by a narrow projecting girdle. The remain- 

 ing segments are about as long as broad except for five or six at the distal end which are 

 shorter. They are rounded off to, and narrower at, each end than in the middle, where 

 they are encircled by a narrow projecting girdle. They are somewhat barrel-shaped. 

 The articular faces are very broadly oval, the long axes of those at the opposite end of 

 each columnal at right angles to one another. The columnals are of a coarse texture like 

 the ossicles of the crown. 



The sides of the basal cup are strongly rounded. Its height is equal to about half its 

 diameter at the distal end. The distal corners of the basal plates are deeply cut away to 

 receive the radials. The crown is damaged on one side and one ray has been broken 

 away: it must be the right posterior ray, for there is no sign of the radianal plate against 

 any of the other radials. In three rays that are complete the arms are of two, or some- 

 times three, brachials. They curl in above the apices of the orals. 



The surfaces of the lower part of the oral plates are only a little sunken below the 

 level of those of the basals, the radials, the costals and the axillaries with which their 

 edges are in contact. The texture of all the plates is coarse but that of the orals coarser 

 than any ; the surface of the proximal part of each is deeply pitted and some of the pits 

 carry pale yellow spherical bodies which must be the glandular sacs known from the 

 posterior end of the embryo (Mortensen, 1920, p. 52, pi. xxiv, fig. 2). In preparations 

 of embryos slightly older than that figured by Mortensen I have seen the sacs lying close 



