94 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Excluding obviously young individuals, specimens of Z. microdiscus have 65100 

 arms, the average number being 71. The arms are 85-145 mm. long, averaging 118 

 mm. in length. In Z. elegans the arms are 26-80, though almost always between 35 

 and 45; the average number is 41. The length is 70-110 mm., averaging 99 mm. 

 The number of the cirri is about the same in both forms. 



In Z. microdiscus the number of cirrus segments is 30-70, usually varying between 

 45 and 55; the average number in fully developed cirri is 47. The length of the 

 cirri is 37-55 mm., averaging 42 mm. In Z. elegans the number of cirrus segments 

 is 30-56, usually varying between 35 and 45; the average number in fully developed 

 cirri is 42. The length of the cirri is 25-38 mm., averaging 32 mm. 



In Z. microdiscus Pj is 20-32 mm. in length, averaging 24 mm., and is composed 

 of 25-60 segments, the average number being 44. In Z. elegans P D is 14-18 mm. 

 long, averaging 16 mm., and is composed of 27-40 segments, averaging 33. 



There can be no reasonable doubt that Hyponome sarsi is the detached visceral 

 mass of Zygometra microdiscus. It is identical with the visceral mass of this species 

 only, and Zygometra microdiscus is common in the type locality of Hyponome sarsi. 

 Since Antedon microdiscus of Bell, 1882, is the same species as that presented by the 

 fragment described as Hyponome sarsi by Loven in 1869, the proper course would 

 seem to be to recognize the species as Hyponome sarsi and to reduce Antedon micro- 

 discus to the status of a synonym. But while there can be no reasonable doubt of 

 the identity of Hyponome sarsi and Antedon microdiscus at the same time no wholly 

 conclusive proof of such identity is possible. So it has seemed best to retain the 

 name Zygometra microdiscus for this species, admitting that so far as can be deter- 

 mined it is quite the same as the species represented by the fragment described as 

 Hyponome sarsi, and admitting also that complete and definite proof of such identity 

 is lacking. 



Localities. Hamburg Southwest Australian Expedition station 16; Shark Bay, 

 Western Australia, northwest of Heirisson Prong; 11-12.5 meters; bottom rocky, 

 with coral; September 13, 1905 [A. H. Clark, 1911] (2, Berl. M., 5966, 6136). 



South Passage, Shark Bay; 9 meters; Hamburg Southwest Australian Expedi- 

 tion, June 16, 1905 [A. H. Clark, 1912, 1913] (1, H. M.). 



Lewis Island, Dampier Archipelago, Western Australia [A. H. Clark, 1913] 

 (2, B. M.). 



Lagrange Bay; 9-15 meters; H. L. Clark, September 1929 [H. L. Clark, 1938]. 



Broome; H. L. Clark, August and September 1929 and June 1932 [H. L. Clark, 

 1938]. 



Mjoberg's station 13; Broome, Western Australia; on the beach at low tide; 

 July 27, 1911 [Gislen, 1919, 1924]. 



Baudin Island, northwestern Australia; 15-27 meters [A. H. Clark, 1929] 

 (2, B. M.). 



Holothuria Bank [A. H. Clark, 1913] (1 + , B. M.). 



Nicol Bay, northwestern Australia; H. M. S. Alert [Bell, 1884; P. H. Carpenter, 

 1888; A. H. Clark, 1911, 1913] (2, B. M.). 



Mermaid Strait; Gazelle [A. H. Clark, 1909, 1911; Hartmeyer, 1916] (1, Berl. M., 

 5607). 



