A MONOGRAPH OP THE EXISTING CBINOIDS 187 



larly modified. These two groups are distinguished from each other by the number 

 of the segments in the proximal pinnules. In one group (including H. sol and H. 

 magnipinna) the stout proximal pinnules have about 30 segments and taper slowly 

 distally to a delicate tip, while in the other (including H. robustipinna and H. martensi) 

 they are composed of about 20 segments and taper very rapidly. These two groups 

 seem quite distinct; but it may be mentioned that in a specimen of H. robustipinna 

 from the Kei Islands Reichensperger found P D to be composed of 22-24 segments. 



Each of the three groups is represented in the Malayan region from the Philip- 

 pines to the Kei Islands by H. bartschi, H. magnipinna, and H. robustipinna. But 

 the two species included hi each of the three groups always have distinct ranges that 

 do not overlap. Thus H. persica is the western representative of the East Indian H. 

 bartschi, H. sol is the western representative of H. magnipinna, and H. martensi repre- 

 sents the widely spread H. robustipinna at Singapore and in British North Borneo. 



With the exception of H. robustipinna, specimens of all the species from any one 

 locality are very uniform in their characters. But H. robustipinna, which appears 

 to have the most extensive range of all the included forms, seems to be very variable. 

 This variation does not seem to be geographical, for Reichensperger has pointed out 

 that a specimen from the Philippines (the type of my H. robustipinna) is unquestion- 

 ably the same as Hartlaub's specimen (the type of Antedon kraepelini) from Burma, 

 and at the same time he recorded two specimens from the Kei Islands in one of which 

 P D has 22-24 segments while in the other it has only 18-20 segments. 



The species of the genus Himerometra are among the very largest of the tropical 

 comatulids, being exceeded in size, when fully developed, only by the largest species 

 of Comasteridae and perhaps by Pontiometra andersoni in the Colobometridae. They 

 are all inhabitants of very shallow water, none having been recorded from a depth 

 greater than 57, or possibly 66, meters. Specimens of all of them have been taken 

 in shore collecting, although they are commonest a few meters beneath the surface. 



History. The genus Himerometra was first proposed, with the genotype Antedon 

 crassipinna Hartlaub, 1890, in a revision of the old genus Antedon published by me in 

 1907. At that time it was considered as including all the multibrachiate species of 

 comatulids with unplated ambulacra except those in the family Comasteridae and 

 those assigned to the genera Zygometra, Pontiometra, and Cyllometra, which were 

 described at the same time; a few 10-armed species, now placed in the genera Amphi- 

 metra and Oligometrides, were also assigned to it. 



In a revision of the family Himerometridae published in 1909 the genus Himero- 

 metra, by the removal of various species to the new genera Amphimetra, Cenometra, 

 Craspedometra, Stephanometra, Heterometra, and Dichrometra, was restricted to its 

 present limits, except only that Himerometra philiberti (J. Miiller) was retained in it 

 with a query. 



KEY TO THE SPECIES IN THE GENUS HIMEROMETRA 



a 1 . Enlarged proximal pinnules very stout with all, or nearly all, of the component segments broader 

 than long, or at least as broad as long; none of the segments in the proximal pinnules are 

 carinate; following pinnules without carinate processes on the earlier segments. 

 6 1 . Enlarged proximal pinnules with about 30 segments, very stout basally and distally tapering 

 gradually to a delicate and more or less flagellate tip; the distal edges of the segments in the 

 middle half or proximal two-thirds of the proximal pinnules are swollen and may be strongly 

 everted, but they are always smooth, never spinous. 



