A MONOGRAPH OF THE EXISTING CRINOIDS 341 



Amphimetra A. H. Clark, Proc. Biol. Soc. Washington, vol. 22, 1909, p. (diagnosis; genotype 

 Comahda [Aleclo] milberti J. Mtiller, 1846), p. 175 (referred to the Hiinerometrinae); Proc. 

 U. S. Nat. Mus., vol. 40, 1911, pp. 2, 13 (common to southeastern Africa and Ceylon; absent 

 from Arabian Sea); Mem. Australian Mus., vol. 4, 1911, pp. 731, 732 (in keys), p. 734 (key to 

 Australian species), p. 764 (original reference; characters; range); Crinoids of the Indian Ocean, 

 1912, p. 10 (purely tropical species do not extend north of Formosa), p. 11 (represented in 

 Ceylon region; this the western limit of the large and highly multibrachiate species [Hetero- 

 metra]), p. 12 (represented in southeast African region [Helerometra]) , p. 21 (found throughout 

 the range of the family Himerometridae [with certain species of Helerometra included]), p. 56 

 (in key), p. 107 (original reference; synonymy). — Hartlatjb, Mem. Mus. Comp. Zool., vol. 27, 

 1912, p. 371 (discussion). — A. H. Clark, Unstalked crinoids of the Siboga-Exped., 1918, p. 73 

 (in key; range), p. 82 (key to the included species).— Gislen, Kungl. Svenska Vet.-Akad. 

 Handl., vol. 59, No. 4, 1919, pp. 3, 23; Zool. Bidrag Uppsala, vol. 9, 1924, p. 88 (synarthrial 

 tubercles); Kungl. Fysiogr. Sallsk. Handl., new ser., vol. 45, No. 11, 1934, pp. 18, 44, 46. — 

 Boone, Bull. Vanderbilt Marine Mus., vol. 7, 1938, pp. 122, 123. 



Comatula (Antedon) (part) A. H. Clark, Bull. Mus. Hist. Nat., Paris, 1911, p. 251 (from P. H. 

 Carpenter, MS.). 



Actinometra (part) A. H. Clark, Smithsonian Misc. Coll., vol. 61, No. 15, 1913, p. 75 (B. M., MS.). 



Helerometra (part) Gislen, Zool. Bidrag Uppsala, vol. 9, 1924, p. 39, footnote. 



Diagnosis. — A genus of Himerometridae in which the arms are normally 10 in 

 number with the brachials beyond the proximal portion of the arms very short with 

 parallel, or approximately parallel, ends; the cirri are of moderate length with all, 

 or at least the outer, segments broader than long, and bear conspicuous dorsal spines 

 or tubercles in the distal portion; the enlarged proximal pinnules, though stouter and 

 somewhat longer than those following, are not especially distinguished ; they are only 

 very slightly, if at all, carinate basally, and the outer ends of their distal segments 

 are usually smooth, though they may bear fine spines. 



Occasional individuals of certain forms may have more than 10 arms, in which 

 case the IIBr series are 2 instead of 4 (3+4), as in the other genera of Himerometridae. 



Geographical range. — From southern Japan southward to the Philippines, Tonga 

 and Fiji, Port Molle, Queensland, and between Fremantle and Geraldton, Western 

 Australia, and westward to the Maldive Archipelago. 



Bathymetrical range. — From the low-tide mark — sometimes even the intertidal 

 zone — down to 109 (?183) meters. The species of Amphimetra are especially charac- 

 teristic of the zone from the low-tide mark down to about 50 meters. All the eight 

 species and forms have been taken in shore collecting, and Prof. Sydney J. Hickson 

 told me that at Macassar he had found a 10-armed comatulid (undoubtedly a species 

 of this genus) hanging from the piling of a dock just above the water at low tide. 

 Only half of the total number of species are known from a depth greater than 50 

 meters, and only one is known from a depth exceeding 100 meters. 



Remarks. — The genus Amphimetra includes eight forms, three of which {tessellata, 

 discoidea, and papuensis) are herein treated as geographical races of a single specific 

 type. Two species, enstfer from Singapore and laevipinna from southern Japan, 

 appear to be quite distinct from each other and from all the rest. The remaining 

 forms, though very distinct when typically developed, approach each other more or 

 less closely or even intergrade so that their real status is not as yet wholly clear. 



The very large and stout tessellata, characteristic of the area from the Sunda Straits 

 to the Moluccas and Kei Islands and the coast of Western Australia, to the eastward 

 passes into the smaller and slenderer discoidea, which is characteristic of the Queens- 



