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



and all subsequent axillaries are articulated, and not united by syzygy as in Actino- 

 metra typica and its allies. Furthermore, the first syzygy in the free arms is not 

 between the first two brachials, as in Actinometra typica and Antedon inwqualis, but 

 in the second brachial as in Actinometra Jimbriata and Actinometra multiradiata 

 (PI. LXII. fig. 3 ; PL LXVI. fig. 1), or in the third as in Actinometra parvicirra and 

 Actinometra divaricata (PI. LXI. figs. 1,5; PL LXIII. fig. 6). 



The numerous species of this series thus fall into two very well defined groups, each 

 of which contains forms with no axillary beyond the distichal, and others with two or 

 sometimes with three. 



The first arm-syzygy in the second brachial, . . . . . .0. Jimbriata. 



The first arm-syzygy in the third brachial, . . . . . .7. parvicirra. 



7. The Fimbriata-grou]}. 



Tridistichate species with a pinnule on the first brachial and a syzygy in the second. 

 The palmar and post-palmar series, when present, consist of two joints, the first bearing 

 a pinnule, and the second axillary with a syzygy. 



Remarks. — The position of the first brachial syzygy in this group is altogether an 

 anomalous one. In ordinary Comatulee the third and fourth joints of the primitive arm 

 become closely united by suture, eventually forming a syzygy, while the pinnule of the 

 former remains undeveloped, like that of the first brachial. But in the Fimbriata- 

 group the first joint above the distichal and every subsequent axillary, whether it be a 

 palmar or a free brachial, bears a pinnule ; and the syzygial union occurs between the 

 primitive second and third brachials, instead of between the third and fourth (PL LX. 

 fig. 1 ; PL LXII. fig. 3), i.e., there is a syzygy in the second instead of in the third 

 brachial of the mature arm. When, however, there are no distichals, so that the arms 

 spring directly from the radial axillary, we usually find a reversion to the more primitive 

 type, with a syzygy in the third brachial, i.e., the epizygal of this syzygy bears a single 

 arm, instead of being an axillary (PL LX. fig. 2 ; PL LXVI. fig. 1). I have very rarely 

 met with any instance of a pinnule on the first and a syzygy in the second brachial 

 above a primary radial axillary. As a general rule this arrangement only occurs after 

 a secondary or tertiary axillary (i.e., distichal or palmar). 



The Fimbriata-gmu]) is only represented in the genus Antedon by a single species, 

 Antedon porrecta. It includes a considerable variety of specific forms, all of which, 

 with two exceptions, are limited to the Indian Ocean, the Eastern Archipelago, and 

 the North-west Pacific. Actinometra lineata and Actinometra discoidea were dredged 

 by the "Blake" in the Caribbean Sea, while the former was likewise found by the 

 Challenger at Bahia. It possibly ranges down to 88 fathoms, while Actinometra 



