PENTACRINOID LARVAE • 219 



columnal is much bigger than in any of the younger stages : it is more than one-third 

 as long as broad. Long cirri of about 15 segments, which reach the ends of the radials, 

 arise from it in all radii but the posterior in which there is only the beginning of a cirrus, 

 about one-quarter the length of the basal plates. The second segment is as wide as the 

 first but it is short. The third and fourth are narrower and they are discoidal. The 

 column is otherwise similar to those of younger stages. 



The basals are longer in proportion to the radials than in No. 18. In other ways the 

 crown resembles that of No. 18. The only complete arm is of 22 brachials with pinnules 

 arising from the eleventh and succeeding brachials. There are very strong side- and 

 cover-plates along the arm and pinnule ambulacra and a few irregularly arranged 

 sacculi along the arms. 



20. Length of crown 9 mm. (Fig. 24^); length of column 13 mm. 



The stem is of 38 columnals and a large lobed terminal plate. The first columnal is 

 not so big as in No. 19 but its cirri, of which there is a single radial whorl, are longer 

 though they are of unequal lengths. The anterior and left anterior are of about 22 seg- 

 ments and reach to the first brachial ; the right anterior is somewhat shorter ; the left 

 posterior is broken ; the right posterior is a rudiment one-third as long as the basal plate. 

 The cirri arise from sockets which incise the columnal for its entire length. The second 

 columnal is as wide as, and longer than, the first. There are indentations in both its 

 proximal and distal margins opposite the larger cirri of the first columnal. The remainder 

 of the column resembles that of slightly younger specimens. The columnals of the 

 middle part of the stem are each encircled by a narrow median girdle. 



The crown resembles those of Nos. 18 and 19. A glandular sac occurs in a pit in the 

 surface of one of the axillaries as well as in the orals. 



The arms are of 19 brachials. Pinnules of up to nine or ten segments occur on the 

 ninth and succeeding brachials ; the lower pinnules are not yet beginning to form. There 

 are strong side- and cover-plates, of the same nature as those of the adult Notocrimis 

 virilis along the ambulacra. There are a few irregularly arranged sacculi along the arms. 



13-2 



