294 THE VOYAGE OF H.M.S. CHALLENGER. 



The amount of carination of the lower pinnules varies considerably, just as it does in 

 Actinometra solan's (PI. LIII. figs. 3-22). As a general rule the first pair of pinnules 

 have their basal joints somewhat produced towards the dorsal side, and in the next two 

 pairs the second and third joints have rather prominent keels, traces of which are some- 

 times visible as far as the twelfth or fifteenth brachial. The terminal comb, which is 

 very well developed on the basal pinnules, becomes gradually smaller and disappears 

 about the sixth or seventh brachial. 



The visceral mass of Actinometra paucicirra, like that of Actinometra Solaris, which 

 occurs at the same locality, is somewhat readily detached from the calyx, and it was 

 occasionally dredged in an isolated condition. It is not so completely plated as that of 

 Actinometra Solaris often is. For the ambulacra are unprotected, and the interradial 

 areas are covered by larger and more nodular plates than in the latter species (Part I., 

 pi. liv. figs. 10, 11 ; pi. lv. fig. 1). Both species, however, may sometimes have the 

 calcareous deposits considerably reduced in extent, though they are rarely entirely absent 

 (Part I., pi. lv. fig. 2). The figured specimen of Actinometra paucicirra shows a small 

 Anilocra living in the anal tube. 



One tetra-radiate individual of this species occurred among all those dredged by the 

 Challenger. An examination of the disk shows that the anterior ray A is missing, so 

 that the mouth comes to be interradial, between the radii E and B, while the anus as 

 usual lies between C and D. The only other species which presents the same arrange- 

 ment of the arm divisions as occurs in Actinometra paucicirra is a new form from Mergui, 

 which differs from it in having normally two, and sometimes three, postradial axillaries, 

 and also in the presence of some thirty cirri on the centro-dorsal. 



3. The Typica-grouj). 



Tridistichate species with the radial axillaries and all the post-distichal axillaries 

 united to the preceding joints by syzygy. 



Remarks. — This group contains four of those abnormal species in which the two 

 outer radials and the first two joints above the distichal and every subsequent axillary 

 are respectively united by syzygy ; while the distichal series itself consists of the usual 

 three joints, with the axillary a syzygy. They are all confined to the Eastern Archipelago 

 and Western Pacific, three of the four being purely littoral species ; while Actinometra 

 typica was also obtained by the Challenger in the neighbourhood of Fiji, from a depth of 

 over 200 fathoms. The rays of this species, and also those of Actinometra multibrachiata 

 divide very frequently, the number of postradial axillaries being sometimes as many as 

 seven (PI. LVI. fig. 3 ; PI. L VII. fig. 1) ; whereas in Actinometra distincta there is no 



