ZENOMETRINAE 163 



There are no oral pinnules : Pi and P^ are absent from all arms of both specimens. 

 The first pinnule is Pj , which arises from the outer side of the fifth brachial and carries 

 a gonad. There are two, three, or more usually four, genital pinnules on each side of 

 the arm. The gonad on the outermost genital pinnule, and more rarely that on Pa , may 

 be small. None but the smaller outer genital pinnule has an ambulacral furrow; the 

 course that the furrow would follow, if present, on the other genital pinnules is shown 

 by a double line of pigment. Pg is of 8 segments, about 4 mm. long. The first segment is 

 slightly longer than broad ; the second is about one-and-a-half times as long as broad. 

 The remaining segments are long. The third and fourth are about four times as long as 

 broad. The distal segments (but for the terminal, which is shorter and pointed) are as 

 long but more slender. The other genital pinnules are similar but of more segments and 

 slightly longer: P3 is of 9 segments, more than 4 mm. long (Fig. 9 d) ; P4 is of 9 segments 

 and 5 mm. long. 



The distal pinnules are of about 1 5 segments and 7 mm. long. The first segment is 

 broader than long, the second about as long as broad ; the articulation between them is 

 greatly widened. The other segments are about four times as long as broad, becoming 

 slightly longer and more slender distally; the articulations are swollen and the distal 

 ends of the segments are everted and spinous. 



The species is brood-protecting: on each genital pinnule there is a brood-pouch as 

 well as an ovary. It does not lie alongside the ovary as in some other brood-protecting 

 species, but somewhat to the side of and distal to it. The ovary lies on the third and 

 fourth segments of the genital pinnule and, in dorsal view, projects farther on the side 

 away from the arm from which the pinnule springs than on the other. The brood-pouch 

 lies along part of the fourth, along the fifth and a part of the sixth, segments and pro- 

 jects more on the side towards the arm from which the pinnule springs than on the 

 other (Fig. 9 d). On some pinnules the brood-pouch is empty. Two in which it is not 

 have been cleared and mounted. In each there are two or three small eggs, o-io mm. 

 in diameter, in the proximal corner of the ovary. In one the remainder of the ovary 

 appears to be occupied by one enormous egg. In the other there are five large eggs of an 

 irregular oval shape, two about 0-25 mm. long, the other three much larger, the largest 

 0-62 mm. long by 0-36 mm. broad. The brood-pouch of the first contains one large egg 

 with no trace of skeletal plates to be seen within it ; in the other there are two, the largest 

 of which is 0-67 mm. long by 0-51 mm. broad. 



A third genital pinnule which was examined, a P3 , shows how far this species protects 

 its brood (Fig. 9 d). The ovary contains a small number of large eggs like those already 

 described, and perhaps some small eggs; in the brood-pouch is one young pentacrinoid 

 larva, ca. 1-3 mm. long, its crown consisting of two closed circles of plates, the basals 

 and orals, in contact with one another, its stalk of ten or more stout joints and a large 

 terminal plate. It lies with its crown against the ovary, the end of its stalk against the 

 sixth segment of the pinnule. Whether this stage represents the farthest to which the 

 pentacrinoid larvae develop before being released from the brood-pouch cannot be said. 

 None is attached to any part of either specimen. 



6-2 



