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



and may divide four, or rarely five, times. Three distichals, the axillary with a syzygy ; 

 palmars, when present, two-jointed without a syzygy on the outside of the ray, but three- 

 jointed with a syzygy on the inside. The first and second post-palmars, when present, 

 also three-jointed, the axillary with a syzygy. 



Forty-five arms ; the anterior ones of a hundred and twenty slightly overlapping, 

 triangular joints which gradually become quadrate ; the hinder arms shorter, with only half 

 as many joints. Syzygies in the third, twelfth, and sixteenth brachials, and then at 

 intervals of three joints. 



The distichal pinnule is relatively long and stout, reaching 13 mm., and that on the 

 second post -palmar, which is but little smaller, is nearly twice the length of that on the 

 second brachial. Those of the next three joints are still smaller, after which the size 

 again increases, but the terminal pinnules are not specially long. The first few pinnules 

 have a well-marked comb, which becomes gradually weaker and is lost after the tenth 

 brachial. Mouth interradial; disk naked; some of the hinder arms have very faint 

 grooves and others none at all. 



Colour in spirit. — light reddish-brown. 



Disk 15 mm.; spread 21 cm. 



Locality. — Band a, 17 fathoms. One specimen. 



Remarks. — This is an elegant little species, which differs altogether from Actinometra 

 belli in having its post-palmar series like the distichals instead of being only two-jointed 

 (PL LXIV. figs. 1, 3). They occur on all the rays but one, and in the anterior half of 

 the ray regeneration has taken place to such an extent that there is a fifth post-radial 

 axillary. As this is probably not the normal condition I have put brackets round the 

 figure which indicates it in the specific formula. 



The great difference in length between the anterior and posterior arms of this type is 

 very striking, the more so as most of the hinder arms have grooves, though only faint 

 ones. The five hinder arms of the E ray are, however, altogether devoid of ambulacra, as 

 the groove which should supply them suddenly stops quite short on the disk at the base 

 of the distichium ; and the right or western curve of the horse-shoe passes by them 

 altogether, on its way to the posterior or D ray. 



7. Actinometra nobilis, n. sp. (PI. LXV.). 



2 



Specific formula — a. 3. g-.( — J. 3. 3. -y. 



Centro-dorsal a thin disk, with about ten marginal cirri in immature individuals ; 

 more or less stellate and rather below the level of the radial pentagon in the adult. 

 Second and third radials short and closely united laterally. The two first distichals of 



