1879.] the Comatulse of the " Challenger" Expedition. 385 



Of these 111 species, 59 belong to the genus Antedon, 48 to Actino- 

 metra, 1 to Ophiocrinus, and 3, which are peculiar in having ten rays 

 to the calyx instead of only five, to a new genus for which I propose 

 the name Pwmachocrinus (7rp6/biaxo?, " Challenger.") It may be 

 thought that this peculiarity is hardly a sufficient reason for the 

 erection of a new genus to receive these three species. It is, however, 

 a much more striking one than that on which the genus Ophiocrinus 

 is based, viz., the presence of five arms only, as the rays, unlike those 

 of most Comatulce, do not divide but bear the arms directly. In Pro- 

 machocrinus on the other hand, there are ten distinct rays, the radial 

 pentagon which is in contact with the centrodorsal consisting of ten 

 separate pieces, and not of five only, as in Ophiocrinus and in the other 

 Comatulce. 



In two of the species the rays are undivided as in Ophiocrinus ; but 

 in the third they divide, as in our common Antedon rosacea, so that 

 there are twenty arms. 



This character, the presence of ten rays, is evidently not an acci- 

 dental one, like the existence of more or less than five rays in other 

 Comatulce and in Phizocrinus. In the latter genus individuals with 

 four to six rays are common, and cases of seven, though rare, 

 may occur. Among the Comatulce, however, it is very different. 

 I have carefully examined three large Comatula collections besides 

 that of the " Challenger," viz., those of the British and Paris Museums, 

 and Professor Semper's collection from the Philippine Islands. Out 

 of the nearly 200 species contained in these collections I have found 

 but two specimens in which there are not five rays in the calyx. In 

 one of these there are only four, and in the other six rays, though in 

 other individuals of each species there are five, the normal number. 



The distribution of Promachocrinus is as follows : — 



P. Kerguelensis (20 arms). Balfour Bay, Kerguelen, 20 — 60 fathoms. 



Royal Sound ,, 28 fathoms. 

 Cape Maclear „ 30 ,, 

 Heard Island 75 ,, 



P. ahyssorum (10 arms). Station 147 1,600 ,, 



„ 158 1,800 



P. Naresii (10 arms). „ 214 500 „ 



Ophiocrinus was obtained at four localities at depths varying from 

 565 to 1,070 fathoms, two in the South Pacific, off South Australia 

 and New Zealand respectively, and two in the North Pacific, one off 

 Japan, and one just north of the Philippine Islands. All the speci- 

 mens belong to one species, which is by no means so slender and 

 graceful as Semper's Philippine species from shallower water, but 

 has a much more massive arm skeleton. 



Among the numerous species of Antedon (59) and Actinometra (48) 



