ISOMETRINAE 183 



Cirri XXXVII-XLVII, in one LX; 25-35. They are very like those of /. vivipara 

 except that the segments are not so numerous and fewer of them are longer than broad 

 (Fig. 1 6 a). The opposing spine is strong and erect, the terminal claw short and strongly 

 curved. 



The radials and primibrachs are of the same shape as in /. vivipara. In the three smaller 

 specimens the radials are nearly as long as the costals in their mid-line but in the others 

 they are shorter. The axillary may make a slight shoulder-like projection with the costal 

 where it incises it. In an arm of one male the radial, costal and axillary are represented 

 by one ossicle considerably shorter than the sum of those three ossicles on adjacent 

 arms. The primibrachs and the first two brachials have sharp and nearly straight side 

 edges. The brachials throughout the arm are of a similar shape but they are altogether 

 less smooth. Those between the first and second syzygies have raised distal edges 

 produced into small thorns and they are slightly waisted. The distal edges of the middle 

 brachials, and even more of the outer, are raised and produced into very strong thorny 

 ridges (Fig. 166). 



The first and second syzygies are usually between the third and fourth and the ninth 

 and tenth brachials respectively but there are as many irregularities in proportion to the 

 number of the specimens as in /. vivipara. 



The pinnules differ from those of /. vivipara. Pj is longer and stouter, sometimes 

 much stouter, than Pj (Fig. 16 c). P3 is a genital pinnule in most if not all of the arms 

 of both males and females. Pj is of 9-14 segments and 5-7 mm. long; the first four to 

 six segments are attached to the disk and are in some specimens much heavier than those 

 which follow, and they are in one compressed from side to side. Po is of 7-10 segments, 

 3-5-5 mm. long; its first two to four segments are attached to the arm by a web of tissue. 



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

 panded as in /. vivipara. Because the ends of the arms are broken it is impossible to say 

 how far the genital pinnules usually extend. In one of the smaller specimens, a female, 

 they end at P13 , but in a larger male they extend beyond Pig . The following are the 

 numbers of segments and the lengths of some genital pinnules: 



In the males the expansion of the third and succeeding segments of the genital 

 pinnules is greater and more asymmetrical, being mainly on the aboral side, than in 

 /. vivipara. In the females the expansion is confined even on the largest — the middle — 

 genital pinnules to the third and fourth segments (Fig. 16 d, e). 



The segments of all pinnules, except those of Pi and perhaps some of those of Pg , 

 have strongly thorny distal edges. On the expanded segments of the genital pinnules 

 the thorniness is confined to the mid-line and the adoral side of the distal edges ; it is 

 absent from the aboral side where nearly all the expansion lies. 



