ME. P. H. CAEPEXTEE OX THE GEXTJS ACTIXOMETBA. 59 



diameter. In the fifth and sixth the proportion between the length and breadth reaches 

 3:2; and a very slight degree of lateral compression is visible in the latter segment, 

 Avhile the fifth, like the four basal segments, is cylindrical, or nearly so. These are the 

 two longest segments of the cirrhus ; and from this point onwards the length of the 

 segments gradually decreases, until in the tenth and following segments ft becomes 

 again less than the dorso-ventral diameter. At the same time the transverse diameter, 

 which in the first five cylindrical segments is equal to the dorso-ventral diameter, under- 

 goes in the seventh and eighth segments a sudden decrease. A faint indication of this 

 is seen in the sixth segment, and it is continued on to the end of the cirrhus, so that its 

 terminal portion exhibits a considerable degree of lateral compression. In correspond- 

 ence with this, a small spine gradually developes itself on the dorsal margins of the sixth 

 and successive segments, on which it becomes progressively more and more marked, 

 until in the penultimate segment, i, e. the last one before the claw, it becomes the short 

 pointed opposing process above mentioned. This series of small spines, like the single 

 penultimate opposing process of the cirrhi of Ant. rosacea, seems to be characteristic of 

 those cirrhi only which have reached their full development ; for scarcely any trace of it 

 is visible in the still immature cirrhus represented in PI. III. fig. 8 c. Although its 

 penultimate segment shows a faint indication of an opposing process, the dorsal margins 

 of the segments immediately preceding it are almost, if not quite, even. 



The segments of this cirrhus, although of the normal proportions, are not so large as 

 those of an adult cirrhus, and (counting the terminal claw) are II in number, the first 

 seven of which precisely resemble those of the cirrhus represented in PI. III. fig. 8 a, 

 with 12 segments and a chaw, so that the extra one in the former case would appear to 

 be interpolated between the middle and end of the cirrhus. As in Ant. rosacea, and for 

 precisely the same reason, greater facility of flexure, the ligamentous substance between 

 the terminal segments is thicker on the aboral side than on the oral (PI. III. ficr. 9 b), 

 while in the more cylindrical segments of the basal half of the cirrhus the ligamentous 

 substance is tolerably equally developed on both sides (fig. 9 a). In correspondence with 

 this, the canal {cc) which occupies the centre, or nearly so, of the circular opposed 

 faces of the basal segments (fig. 9 a), lies in the laterally compressed terminal segments 

 much nearer to the oral side of the oval articular faces, more than half of which is 

 occupied by the large fossa for the lodgment of the aboral interarticular ligament 

 (fig. 9 b). The opening of the central canal (c c) is surrounded in each case by a more or 

 less prominent articular surface. 



(§ 39) Both the single specimens of Varieties 3 and I of Act. pohjnwrpha which 

 I have been able to examine had unfortunately lost all their few cirrhi ; but in Var. 1 

 twenty-five still remained attached to the centro-dorsal piece ; most of these are fully 

 developed, and present some slight differences from those of the type (PI. III. fig. 11). 

 Not only is the number of segments greater, varying usually from 13 to 15, besides the 

 terminal claw, but they also differ considerably in their relative proportions ; for in the type 

 the fifth and sixth segments are the longest, while in Var. 1 there is less difference between 

 them and the fourth and seventh in this respect. The lateral compression, which is not 

 visible till the eighth segment, becomes somewhat marked towards the end of the cirrhus, 



SECOND SERIES. — ZOOLOGY, VOL. II. 9 



