766 "THETIS " SCIENTIFIC RESULTS. 



AMPHIMETRA DISCOIDEA (A. H. Clark). 



Comalula dibrachiata, 1862, Dujavdin and Hupe, Hist. nat. des 

 zoophytes, Echinoderms, p. 208 {nomen nudum). 



Antedon milherti, 1884, Bell, Rep. Zool. Coll. H.M.S. "Alert," 

 p. 156 {Port Molle ; Port Denison ; Prince of Wales Channel ; 

 'Torres Strait). — 1885, Proc. Linn. 8oc. iST.S. Wales., vol. 

 9 (1884), p. 497 {Port Denison; Port i/oZ^e).— 1894, Proc. 

 Zool. Soc, 1894, p. 394 {N.W. Australia, 8-15 /??is.). 



Himerometra discoidea, 1908, A. H. Clark, Smiths. Miscell. Coll. 

 (Quarterly Issue), vol. 52, part 2, p. 215 (Port Denison). 



Amphimetra formosa, 1909, A. H. Clark, Proc. U.S. Nat. Mas., 

 vol. 37, p. 32 {Philippines ; nomen nudu7n). — Vidensk. 

 Medd. fi'a den Naturhist. Forening i Kobenhavn, 1909, p. 

 157 (Singapore; Philippines). 



Differential Characters. — So far as known this species never 

 has more tlian ten arms ; the lower pinnules are subequal in 

 length, and all rather short ; the cirri are slender, the segments, 

 at least in the proximal half, being somewhat longer than broad. 

 A. milherti, which also occurs in Australia, has very stout 

 cirri with all the segments much broader than long and sub- 

 equal. 



Specimens in the Australian Museum Collection. — Port Denison 

 — Twelve specimens; one of these has cirri xxii., 46, 30 mm. 

 long; another xx., 36-49, 30 mm. long; a third xxiii., 43, 40 

 nmi. long, a fourth xxii., 42-45, 30 mm. long ; these and five other 

 similar examples exactly resemble the type, which ahso came 

 from Port Denison ; there is no tendency toward the curiously 

 abrupt type of synarthrial tubercle nor the short segmented 

 proximal pinnules characteristic of the form which I have called 

 formosa, from Singapore and the Philippine Islands ; three other 

 large and well developed specimens with cirri about xx., 46-51 

 (niaximuni) 30 mm. to 37 mm. long, however, exhibit the syn- 

 arthrial tubercles and lower pinnules of the type found in A. 

 formosa more or less perfected, and I therefore find myself 

 obliged to consider the two supposed species as only a single 

 form, " forniosa," representing merely a more developed stage 

 than typical discoidea. Port MoUe — Two specimens with cirri 

 about XX., 39-42, 30 mm. long ; both of these have synarthrial 

 tubercles resembling those of the type of A.form>osa. 



Additional Australian Records. — Torres Strait, in 10 fathoms ; 

 Prince of Wales Channel, in 7-9 fathoms ; Holothuria Bank, in 

 15 fathoms; Port Molle, in 12-20 fathoms; Port Denison, in 3 

 fathoms; North-western Australia, in 8-15 fathoms; West 

 Australia. 



