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



Distichal and palmar pinnules large and stout, composed of forty to fifty joints, the 

 second one rather the longer. Their lower joints are large but not specially marked ; the 

 following ones diminish in size, but gradually develop a projection of the dorsal edge 

 at their distal end, which disappears in the smaller terminal joints. The third and 

 following pinnules decrease rapidly both in length and in stoutness, after which the 

 length slowly increases again. 



Disk-ambulacra protected by a well-developed calcareous plating which ceases at the arm 

 bases ; anal tube also considerably plated, but the other interpalmar areas are unprotected. 



Colour in spirit, — skeleton brownish-white, and the perisome mottled with grey. 

 Sacculi very abundant on the pinnules. 



Disk 17 mm., spread about 20 cm. 



Locality. — Station 186, September 8, 1874; Torres Strait; lat. 10° 30' S., long. 

 142° 18' E.; 8 fathoms ; coral mud. One specimen. 



Remarks. — Only one example of the species was obtained by the Challenger, but it 

 did not come into my hands with the rest of the collection, having been given by Sir 

 Wyville Thomson to the National Museum at Stockholm, where I found it in August of 

 last year (1886), and Professor Loven has since been kind enough to send it over to 

 England for my further examination. 



A larger specimen of the same type was obtained in 1881 at Port Molle, Queensland, 

 by H.M.S. "Alert," and was described by Professor F. J. Bell, 1 together with some 

 smaller individuals already in the National Collection from Nicol Bay, Australia. 



There was a very important omission, however, in Bell's description ; for he entirely 



overlooked the fact that the two outer radials are united by syzygy, a character which, 



next to those of the genus, is of primary importance for systematic purposes. His 



description and figure rather led me to suspect the presence of this character long before 



I saw the Challenger specimen, and my suspicions were verified when I examined his 



types for myself. He likewise makes no mention of any axillaries beyond the post- 



palmars, although such must be present to bring the number of arms up to ninety, the 



number which he describes in the adult, while several quaternary arms are represented 



. c 



in his figure. His specific formula must be altered therefore from A.3.3.(3).— . to 



A.R.3.3.3.3.— . 



c 



It is the presence of this fourth axillary above the radials which is one of the 

 characters distinguishing this species from Antedon midtiradiata. I have not seen any 

 specimen without it, though it is much more frequent in the individual from Port Molle than 

 in those from Nicol Bay and Torres Strait. These last resemble one another in Laving a 

 smaller number of cirrus-joints and a better-developed penultimate spine than in the type. 



1 "Alert" Report, p. 163, pi. xv. 



