PART 5 A MONOGRAPH OF THE EXISTING CRINOID3 645 



rows \vhich are regular near the apex but less so near the periphery. The proximal edge 

 is slightly produced interradially. 



The cirri are XXXVII-LX; 25-35. Most of the segments are wider than long. 

 The opposing spine is strong and erect, the terminal claw short and curved. 



In the three smaller syntypes, the radials are nearly as long as the IB^ but in the 

 larger ones they are relatively shorter. The IBr 2 (axillary) may form a slight shoulder- 

 like projection with the IB^ where it incises it. The lateral edges of the ossicles of the 

 IBr series and the first two brachials have sharp and nearly straight sides. The other 

 brachials are less smooth, becoming progressively more thorny towards the distal end 

 of each one. 



The first and second syzygies are usually between brachials 3+4 and 9 + 10 but 

 there are many exceptions to this. 



P! is longer and stouter than P 2 , usually having 10 to 13 segments and measuring 

 4.5 to 7.5 mm. in length; the first four to six of the segments are attached to the disk and 

 may be distinctly heavier than the following segments. P 2 is of 7 to 9, usually 8 seg- 

 ments, 2.5 to 4.5 mm. long; the first two segments are webbed to the arm. In 10 speci- 

 mens measured, PI was over half again as long as P 2 . 



The species is viviparous and the middle segments of the genital pinnules are ex- 

 panded. In the females this expansion is limited to the third and fourth segments but 

 in the males it extends for about five segments and is mainly on the aboral side. P 3 is 

 usually the first genital pinnule but on some arms or specimens it may be P 4 . In the 

 female, P 3 , when it is a genital, measures 4 to 5 mm. and has about 9 segments while 

 in the male it has 10 segments and measures 5 mm. The following genital pinnules 

 increase in length and number of segments; P u of a female has 14 segments and measures 

 8 mm. and P 15 of a male has 18 segments and is also 8 mm. long. The segments of all 

 the pinnules, except those of P] and sometimes also of P 2 , have strongly thorny distal 

 edges. On the expanded segments of the genital pinnules the thorny part is limited to 

 the midline and the adoral side of the distal edges, being absent from the aboral side 

 where the main expansion lies. 



The embryos in the brood pouches were found to be similar to those of Isometra 

 vivipara, the largest having the oral and basal plates in contact with one another and 

 measuring 0.5 to 0.6 mm. in length. 



The ventral surface of the disk, except between the arm bases, is plated, the disk 

 ambulacra being lined by strong plates. At the apices of two of the interradii there are 

 large plates like orals in the single specimen sacrificed for examination, but these appear 

 to be absent from the apices of the other interradii. Otherwise, the interradii are oc- 

 cupied by plates of different sizes. In the anal interradius there are two plates of 

 conspicuous size, one resting on the perisome and the other, in contact and in line with 

 it, on the base of the anal cone, on which there are other plates. In nine other speci- 

 mens some plates could be seen on the disk. 



Sacculi are numerous, regular and conspicuous on the arms and pinnules of the 

 dusky coloured males, but inconspicuous on the others. 



The distal pinnules of some specimens have no ambulacral skeleton, but those of 

 others have reduced side and cover plates. The most elaborate have side plates in the 

 form of rods, which may be simple or forked; the cover plates fan out from a simple stem 

 at the base. There may bo some smooth or knobbed spicules in the tentacles. 



None of the female syntypes bore pentacrinoids on the arms. 



