624 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



pinnules are joined to the disk or sides of the arms by webs of tissue from the first 

 four or five segments. 



The species is viviparous. P 6 is usually the first genital pinnule, rarely P< or P 6 . 

 It has up to 15 segments and is about the same length as the last oral pinnule. The 

 genital pinnules extend to P 13 in smaller specimens, to P 18 in larger ones and the outer- 

 most may be of 18 to 26 segments and 9 to 14 mm. long. The first two segments of the 

 genital pinnules are short and stout with the aboral portions of their distal edges pro- 

 duced into spines. The segments carrying the gonads are much more strongly expanded 

 in the female than in the male. In the smallest specimen, which has arms 35 mm. long, 

 none of the segments of the genital pinnules is expanded. 



In the largest male the testes of the middle genital pinnules lie along the third to 

 eighth segments and they are expanded, more strongly on the aboral than the oral side. 

 The testes of the lower and outer genitals of big males and those of younger males are 

 smaller and, consequently, fewer segments are expanded. The third or the fourth 

 segments are the widest and longest. The remaining segments along which the testes 

 lie decrease in width gradually. The expanded segments are raised into a keel-like 

 ridge in the miclline. The narrow portion of the distal edge which is a part of this 

 ridge may be thorny. The distal segments beyond the gonad are strongly compressed. 



In a small female only the third to fifth segments of the genital pinnules are ex- 

 panded, but in the largest many of the genital pinnules have the third to the seventh 

 segments expanded and in a few pinnules even the eighth. The expansion of the seg- 

 ments of a pinnule may be uneven; sometimes the sixth segment is very narrow on the 

 aboral side with the corner of the fifth segment produced alongside it towards and 

 sometimes meeting the seventh. There may be other irregularities. As in the male 

 the expanded segments are raised into a ridge in the midline. The ovary is a long fusi- 

 form body lying along the adoral side of the pinnule. It is longer than the brood 

 pouch and the strongly expanded segments. In a pinnule where the brood pouch lies 

 along the third to sixth segments, which are strongly expanded, the ovary extends to 

 the eighth segment. In the largest female the brood pouches are empty. In a medium- 

 sized one they are crowded with embryos and so large that they bulge out beyond the 

 edges of the expanded segments. A transverse depression runs across the face of the 

 brood pouch ventrally, which is due to a septum dividing the pouch into two equal com- 

 partments. It appears to act as a support since the contents of the two compartments 

 are similar. In a moderate-sized specimen the proximal compartment of a brood pouch 

 contained fourteen embryos, of which thirteen were young and without skeletal plates. 

 The distal compartment contained ten embryos, also without plates. In a smaller 

 specimen the proximal compartment had four embryos, including one with plates and 

 the distal had three with plates and one without. 



The embryos vary from 0.5 to 0.8 mm. in length. Some of the younger ones are 

 distorted by the lack of space. In the largest the sucking disk and vestibulum are 

 clearly marked; the oral and basal plates are nearly in contact with one another. There 

 are about 20 stem plates and a very large terminal plate. The basal circle embraces 

 the stem. Some of the embryos have bands of cilia around them. 



Most of the distal pinnules are similar in length and number of segments to the 

 outer genital pinnules but they become shorter towards the end of the arm. 



The disk appears to be naked in the few specimens where parts of it can be seen. 

 The anal cone is high. 



