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



Colour in spirit — greyish-green. 

 Disk 8 mm. ; spread 22 cm. 

 Locality. — Tongatabu Eeefs. 



Remarks. — This is a very elegant species which may be distinguished from Actino- 

 metra parvicirra by the characters of its arm-joints. The lower joints lose their 

 triangular shape very soon and become unequally quadrate; the two sides gradually 

 become more equal untd the outline is nearly square, and finally the joints become 

 almost cylindrical with slightly oblique ends. The relative length of the lower joints 

 varies in some of the arms ; that selected by the artist for representation having rather 

 shorter joints than its fellows. 



The small size of the cirri, and their fewness in numbers, will prevent this species 

 from being confounded with Actinometra trichoptera. Some specimens from the Nicobar 

 Islands in the museums at Copenhagen and Vienna should perhaps be referred to it on 

 account of the length of their arm -joints. 



3. Actinometra trichoptera (Valenciennes), Mull., sp. (PI. LXIII. figs. 1-5). 



be 

 Specific formula — a. 3.(3)—. 



Remarks. — This species, like Actinometra parvicirra, may or may not have palmar 

 series, and will therefore be considered later. It was obtained by the Challenger at Port 

 Jackson. 



4. Actinometra divaricata, n. sp. (PL LXIII. figs. 6-8). 

 Specific formula — a.3.2.3.3.— . 



Description of an Individual. — Centro-dorsal stellate, without traces of cirri, and a 

 little below the level of the radial pentagon, the inner sides of which are somewhat cut 

 away. The second radials are relatively long and incompletely united laterally ; the 

 rays are quite free and may divide five times. 



Three distichals, the axillary with a syzygy ; two palmars without a syzygy ; the 

 first and second post-palmar divisions, when present, each of three joints, the axillary 

 with a syzygy. 



Arms very numerous, eighteen or twenty to the ray, and all grooved ; but the hinder 

 arms are only faintly so and are very narrow and short, with one hundred to one hundred 

 and twenty slightly overlapping joints ; the anterior arms have rather more. The lower 

 joints are shortly triangular, becoming more oblong, and finally nearly square. 



Syzygies in the third, twelfth, and sixteenth brachials, and then at intervals of three 

 or four joints. 



