78 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



of the elements of the division series. In color most of them are unique in being 

 scarlet and bright yellow in usually broad alternating bands; but some of them are, 

 and others may be, olive-green, brown, or dull yellow. 



In the genus Zygometra the syzygy between the elements of the IBr series is 

 tough and is almost never broken through during capture. Their numerous arms 

 give these species a striking similarity to species of Himerometridae with which they 

 are easily confused. 



In identifying any multibrachiate comatulid, therefore, the first step after the 

 determination of the presence or absence of a comb on the oral pinnules (the presence 

 of a comb places the specimen at once in the Comasteridae) should always be the criti- 

 cal examination of the articulation between the elements of the IBr series. If this is 

 a fine straight dotted line, indicating the presence of a syzygy, the specimen belongs 

 to some species of Zygometra. It is not long before one becomes very adept at 

 recognizing the species of Zygometra at sight, for they have a very characteristic 

 appearance difficult to define. In the smaller species the usually long sharp spines on 

 the outer cirrus segments distinguish them at once from any of the species of Himero- 

 metridae with which they might be confused, while the large stout cirri of the large 

 Australian species, coupled with the characteristic oral pinnules, are equally diagnostic. 

 Nevertheless it is always possible to confuse the small species with species of Hetero- 

 metra and the large species with species of Himerometra, so that no matter how familiar 

 one may be with these creatures the articulation between the elements of the IBr 

 series should invariably be examined. 



History. In bis report upon the comatulids collected by the Challenger published 

 in 1888 Dr. P. H. Carpenter placed the three forms of Antedon, as understood by him, 

 in which the elements of the IBr series are united by syzygy instead of synarthry 

 (Antedon fluctuans, A. multiradiata, and A. microdiscus) under the heading Antedon, 

 Series I. Although these three forms were the only ones formally included by him 

 under this heading, he said that it is probable Miiller's Comatula tessellata (=Amphi- 

 metra tessellata) belongs also to Series I, though he had never been able to get a sight 

 of the type specimen, it being the only one of all the described species of Antedon if, 

 indeed, it be an Antedon that he had not personally examined. As contemplated 

 by Carpenter, Series I of Antedon, including species in which the elements of the IBr 

 series are united by syzygy, was the equivalent of Series II, including 10-armed species, 

 Series III, including species with IIBr 2 series, and Series IV, including species in which 

 the IIBr series are 4(3+4). In a note written after his account of the forms included 

 under Series I had been printed, Carpenter said that these forms may be considered 

 conveniently as belonging to the Elegans group, named for Antedon elegans, which 

 had been described by Prof. F. Jeffrey Bell in 1884, but in which the occurrence of a 

 syzygy between the elements of the IBr series had escaped notice until after his discus- 

 sion of Series I. 



In his account of the comatulids collected by Dr. John Anderson in the Mergui 

 Archipelago published in 1889 Carpenter further discussed the Elegans group in con- 

 nection with Antedon elegans (Antedon elegans is Zygometra elegans, but the specimens 

 from the Mergui Archipelago represent Z. comata) and described a new species, 

 Antedon (Pontiometra) andersoni, which he said may be for the present referred to the 

 Elegans group. 



