A MONOGRAPH OF THE EXISTING CRINOIDS 81 



be found that are intermediate in practically all their characters. Zygometra andro- 

 meda is simply a highly ornate from of Z. comata. 



The range of the small and generalized Z. comata includes the whole Indo- 

 Malayan region, and it also reaches northwestern Australia. Zygometra microdiscus 

 and Z. elegans are confined to the Australian region; Z. microdiscus occurs in the Aru 

 Islands from which Z. elegans is not known, but Z. elegans extends much farther 

 south on both the east and the west coasts than Z. microdiscus. So far as we know at 

 present Z. punctata is confined to northeastern and northern Australia and the Aru 

 Islands, while Z. pristina has been reported only from the Philippines. 



History. — Prof. Sven Loven's so-called recent cystidean Hyponome sarsi, des- 

 cribed in 1869, was based upon a detached visceral mass of some species of this genus. 

 There can be little doubt that this species was the one later (1884) described by Bell 

 as Antedon microdiscus. Though in all probability Antedon microdiscus, the type of 

 the genus Zygometra, is identical with Hyponome sarsi, the type of the much earlier 

 genus Hyponome (see page 95), no useful purpose would be served by substituting 

 Hyponome for Zygometra. Technically the slight doubt that may be considered to 

 exist in regard to the identity of Hyponome sarsi and Antedon microdiscus may be 

 regarded as sufficient to justify the continued use of Bell's name microdiscus in place 

 of sarsi, and of the generic name Zygometra instead of Hyponome. 



In his report upon the Challenger comatulids published in 1888 Dr. P. H. Car- 

 penter set apart as Antedon, Series I, those species in which the elements of the IBr 

 series are united by syzygy. In this group he included fluctuans, multiradiata, and 

 microdiscus. Later in the same volume he added Bell's elegans, under which he placed 

 fluctuans as a synonym, and also an unnamed species [ = Pontiometra andersoni] 

 from the Mergui Archipelago. Except for the inclusion of the last named, Carpenter's 

 Series I of Antedon coincides exactly with Zygometra as now understood. 



The genus Zygometra was diagnosed and the type species designated as Antedon 

 microdiscus Bell, 1884, in a paper published on October 29, 1907. But in the article 

 just preceding this hi the same volume, which was published on the same day, a new 

 species was described under the heading "Zygometra koehleri, sp. nov." In this 

 volume the description of Zygometra koehleri is found on page 339, while the genus 

 Zygometra is diagnosed on page 347. 



Zygometra koehleri is merely the young of the species now known as Catoptometra 

 hartlaubi, and it might be argued that since the generic name Zygometra was first 

 mentioned in the combination Zygometra koehleri, this form is really the type of Zygom- 

 etra and consequently Zygometra should replace the later Catoptometra as used herein. 

 As nothing would be gained by such substitution, which would certainly result in 

 endless confusion, the generic names Zygometra and Catoptometra are in the foDowing 

 pages used in the sense in which they have been uniformly employed during the past 

 30 years. 



As first proposed, the genus Zygometra included all the species of comatulids with 

 the elements of the IBr series united by syzygy, but in 1908 those species in which the 

 outer cirrus segments are smooth dorsally were removed from Zygometra and placed 

 in the new genus Catoptometra, leaving Zygometra as understood herein. 



