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



a much longer pinnule, the lower joints of which are usually, though not always, 

 enlarged for the support of the genital glands, as in its successors (PL XXIX. fig. 3). 

 After about the twelfth brachial, however, the glands become reduced in size and the 

 pinnule-joints smaller again (PI. XXIX. fig. 4). As in Antedon alternata every alternate 

 brachial above the twelfth is usually a syzygial joint (PI. XXIX. fig. 1 ; PI. XXXII. 

 figs. 5, 7). 



15. Antedon abyssorum, n. sp. (PL XXIX. figs. 10-13). 

 Specific formula — A.—. 



Centro-dorsal conical, bearing about thirty cirri of fifteen to eighteen joints, nearly 

 all of which are longer than wide. 



Three radials visible ; the second partially free, rather convex and very deeply incised 

 for the axillaries. These are shield-shaped or rhombic, as long or longer than wide, with 

 much incurved distal edges. First brachials deeply incised by the irregularly quadrate 

 second brachials. Ten arms of nearly smooth joints, which are almost oblong up to the 

 second syzygy and then become obliquely quadrate. Syzygies in the third and eighth 

 brachials, then about the fourteenth, and afterwards at intervals of one to five joints. 



The first pair of pinnules are slender and delicate, composed of ten or twelve 

 elongated joints, that on the second brachial being rather the longer. Those on the 

 fourth and the ten or twelve following brachials are longer with stouter joints, and 

 support the short and thick genital glands. The later pinnules are much elongated. 



Disk and ambulacra naked ; sacculi tolerably abundant on the outer pinnules. 



Colour in spirit, — dirty white. 



Spread perhaps 6 cm. 



Locality.— Station 147, December 30, 1873 ; kit, 4G° 16' S., long. 48° 27' K; 1600 

 fathoms ; Diatom ooze ; bottom temperature, 34° - 2 P. Eleven specimens. 



Remarks.- — This abyssal form agrees with Antedon angustipinna in the relatively 

 small size of the first pair of pinnules (PL XXIX. figs. 2, 11), but differs from that type 

 in several points. 



There is a smaller number of cirrus-joints, but they are long and slender instead of 

 short and wide ; while there may be from one to five joints between the brachial 

 syzygies, and not one only as in Antedon angustipinna (PL XXIX. figs. 1, 10). In the 

 latter species those lower joints of the genital pinnules which support the glands are 

 considerably thickened ; but this is not the case in Antedon abyssorum (PL XXIX. 

 figs. 3, 12) ; while the later pinnules of this species are much longer than in Antedon 

 angustipinna (PL XXIX. figs. 4, 13). 



