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



Disk 7 mm.; spread about 20 cm. 



Locality. — Station 192, September 26, 1874; near the Ki Islands; lat. 5° 49' 15" S., 

 long. 132° 14' 15" E.; 140 fathoms; blue mud. Eight specimens and two fragments. 



Remarks. — This remarkable species is very readily distinguished from every other 

 bidistichate Antedon, with the exception of Antedon spinifera from the Caribbean Sea, 

 Both types alike have long and spiny cirri ; but those of Antedon quinquecostata are 

 both more numerous and reach a greater length than in the Caribbean species. The 

 latter also has a shortly columnar centro-dorsal, with double rows of cirrus-sockets, 

 though there are frequently only two sockets in each row and not four, as is so often the 

 case in Antedon quinquecostata (PI. III. fig. 6cZ). 



In Antedon spinifera too, the radials, distichals and lower brachials are by no means 

 so sharply carinate as in Antedon quinquecostata, and there is an alternating double 

 row of strong curved spines on the base of each arm. Generally also there are thirty 

 arms, owing to the presence of two palmar axillaries on each ray, while the number in 

 Antedon quinquecostata is typically twenty, though I have found a single palmar 

 series to be present in two separate individuals (PI. XXXVIII. fig. 1). Another point 

 of difference between the two species is that Antedon spinifera has very large and 

 abundant sacculi, while, if present at all, they are most scantily developed in 

 Antedon quinquecostata, as is also the case in some other species from the same 

 station. 



The lateral flattening of the radial axillaries and of the next following joints is less 

 marked in this species than in the Basicurva-gvoup. The first distichal and the first 

 brachial, especially the two on the outer arms of each ray, are the joints which show it 

 most distinctly ; but it is sometimes to be traced as far as the fourth brachials of the 

 outer arms. The pinnules of adjacent second brachials, however, have their lower joints 

 flattened against one another, very much as in Antedon valida (PI. XV. figs. 5, 6), 

 though not cmite to the same extent. The two lower joints of the next few pinnules 

 are somewhat wider and more expanded than their fellows, but this feature disappears 

 in those further out on the arm (PI. XXXVIII. figs. 2, 3). 



The radial pentagon of this type differs somewhat in character from that of most 

 other species of Antedon (PI. III. figs. 6, a-d). Its angles are produced outwards to 

 correspond with the interradial ridges of the centro-dorsal, each of which fits into a 

 notch between the everted lateral angles of two adjacent radials ; and under ordinary 

 circumstances these angles are the only parts of the first radials which are visible 

 externally. The dorsal surface of the radial pentagon is remarkable for showing no 

 signs of any basal star, as there is a very well developed one in Antedon spinifera. The 

 central opening is relatively large, and the rosette within it rather ill-defined, an 

 unusual condition in a tropical species of Antedon. 



