34S SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 50 



Zygometra corresponds to Dr. Carpenter's "Elegans group" or 

 series 1 of Antcdon, and is composed of species occurring from Aus- 

 tralia northward to southern Japan. In regard to this genus the 

 question at once arises as to whether the generic name Hyponome, 

 proposed by Loven, should not be used. Hyponome was founded on 

 a detached visceral mass, probably of Antedon micro disc us, which 

 was considered by Professor Loven to be a recent cystidean, and 

 described as such. Now the characters given for Hyponome sarsii 

 do not permit us to refer it to any species of Zygometra with any 

 degree of certainty; in other words, Hyponome is a genus with a 

 non-recognizable type, and therefore has no standing. 



The following described species are referable to Zygometra; I 

 have examined an additional species from Japan : 



Zygometra clegans (Bell) Zygometra microdiscus (Bell) 



" ' hartlattbi (A. H. Clark) multiradiata (P. H. Car- 



" kcehleri A. H. Clark penter) 



rubroflava (A. H. Clark) 



2. NANOMETRA, gen. nov. 



Centro-dorsal hemispherical, bearing 15 to 25 rather slender cirri 

 with 25 to 30 segments, very uniform, never much longer than wide, 

 the distal sometimes more or less carinate; disk and pinnule ambu- 

 lacra not plated ; costals united by bifascial articulation, short and 

 broad, in lateral apposition, with sharply flattened sides (i. e., "wall- 

 sided") ; the first two or three brachials also have sharply flattened 

 sides ; ten arms, the brachials quadrate, sometimes elongate ; the 

 third and fourth brachials united by syzygy (usually) ; a second 

 syzygy occurs between brachials 9 and 10 to brachials 13 and 14, 

 and syzygia occur distally with 2 to 8 bifascial articulations inter- 

 vening; lower pinnules stout, more or less carinate and prismatic, 

 hut not elongate ; middle and distal pinnules slender, more or less 

 carinate or prismatic, the first two segments short, more or less 

 expanded, the others elongate. 



Color in life, yellow. 



Type of the genus. — Antedon minor A. H. Clark, 1907. 



Nanomctra includes those species of Dr. Carpenter's "Basicurva 

 group" which differ markedly from all the others in entirely lacking 

 the characteristic plating of the disk and ambulacra. They are all 

 small species, inhabiting warm and comparatively shallow water, 

 and are found from the Arafura and Australian seas northward to 

 southern Japan. 



