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



Disk and ambulacra naked ; sacculi fairly abundant, especially on the outer pinnules. 



Colour in spirit, — the skeleton white, with the perisome brownish. 



Disk 4 mm.; spread probably 5 cm. 



Localities.— Station 169, July 10, 1874; lat. 37° 34' S., long. 179° 22' E.; 

 700 fathoms ; blue mud ; bottom temperature, 40° F. One specimen. 



Station 170a, July 14, 1874; near the Kermadec Islands; lat. 29° 45' S., long. 

 178° 11' W.; 630 fathoms ; volcanic mud ; bottom temperature, 39°"5 F. Two specimens. 



Station 218, March 1, 1875; lat. 2° 33' S., long. 144° 4' E.; 1070 fathoms; blue 

 mud ; bottom temperature, 36°"4 F. One specimen. 



Station 236, June 5, 1875; lat. 34° 58' N., long. 139° 29' E.; 775 fathoms; green 

 mud ; bottom temperature, 37°'6 F. Four specimens (two of them young) with 

 Myzostoma cornutum. 



Remarks. — This is another of those very interesting species which are widely dis- 

 tributed in the abyssal region. I was at first inclined to separate the two varieties from 

 the South and the North Pacific respectively (PI. XVIII. fig. 1 ; PI. XXXII. fig. S), 

 but the additional experience of variable specific characters gained between 1879 and 

 1887 has led me to abandon this idea. The axillaries and second brachials of the more 

 northern forms have sharper proximal angles than in the southern variety ; while the 

 joints both of the cirri (PI. XXXII. fig. 9) and of the pinnules (PL XXXII. figs. 5, 7) 

 are relatively longer. Sometimes also the first two or three syzygial intervals after the 

 twelfth brachial consist of two joints (PL XXXII. fig. 8), instead of one only as in the 

 southern variety (PL XVIII. fig. l) ; though in the outer parts of the arms syzygial and 

 simple joints alternate with great regularity (PL XXXII. figs. 5, 7). 



The two young individuals obtained at Station 236 chiefly differ from the more 

 mature form in the relatively greater length of the joints composing the cirri, arms, and 

 pinnules, and in showing more of the first radials externally ; this is especially the case 

 in the youngest specimen, which has not yet developed its genital glands, and is only 

 about 30 mm. m diameter. The appearance of the first radials externally gives the 

 calyx a considerable amount of resemblance to that of Antedon abyssicola from Station 

 244 (2900 fathoms), but this, though absolutely larger, shows more of the radials than 

 appears in the young Antedon alternata, and has fewer joints in its cirri (PL XXXIII. 

 fio-. 1), while the syzygial interval in the outer parts of the arms usually consists of more 

 than one joint. 



The sino-le individual of Antedon alternata which was dredged at Station 218 is 

 peculiar in having four radials on one ray (PL XXXII. fig. 6). So far as it is possible to judge 

 from the characters of the other rays, the third of these seems to be the intercalated joint. 



Antedon alternata is readily distinguished from Antedon tenella and from Antedon 

 exigua by the presence of only one joint between every two successive syzygies in the 



