A MONOGRAPH OF THE EXISTING CRINOIDS 199 



the central column may be wholly or partially absent. After examining an example 

 of the type species, Carpenter's Antedon distincta, in London, Gislen found that the 

 cirri are arranged in 10 columns. This is the chief character of Perissometra, which 

 therefore becomes a synonym of it. Pachylometra offers no other features other than 

 details of ornamentation by which it may be separated from Glyptometra. It there- 

 fore has no standing. Crossometra differs from Perissometra only in having a greater 

 number of arms, a wholly unreliable feature. Calyptometra was distinguished mainly 

 on the basis of the type of ornamentation of the division series and arm bases, a char- 

 acter of wholly minor significance. The elimination of these genera leaves eight genera 

 in the family which seem worthy of recognition — Chondrometra, Monachometra, Glypto- 

 metra, Crinometra, Chlorometra, CJiaritometra, Poecilometra, and Strotometra. 



There seems to be a clear-cut dividing line between the groups of species in which 

 the genital pinnules taper from the usually more or less broadened earlier segments to 

 a delicate tip which is always much longer than the gonads, and those in which the 

 genital pinnules have from two to four segments much broadened, followed by a slender 

 tip which is shorter than the gonads. In the first category the group with the division 

 scries and arms much compressed laterally and rising evenly dorsally to a ridge, Chon- 

 drometra, seems to be quite distinct from the group in which the arms are rounded 

 dorsally, with or without a median raised line. In the latter group Crinometra is dis- 

 tinguished by the relatively long oral and short genital pinnules. In Monachometra 

 and Glyptometra the oral and middle pinnules differ little or not at all in length. In 

 Monachometra there are narrow and strongly developed synarthrial tubercles, the Ilbr 

 series are always 2, and the opposing spine is forked, whereas in Glyptometra the syn- 

 arthrial tubercles are slightly or not at all developed, the IIBr series are usually 4 (3 + 4), 

 sometimes 2, and the opposing spine is single. In the group with the genital pinnules 

 much swollen at the base and with a short distal portion, the long conical centrodorsal 

 with the cirri in five double midradial columns, the opposing spine forked, and about 

 20 arms with the IIBr series 2 distinguishes Chlorometra. In Chlorometra the genital 

 pinnules are not so abruptly and greatly swollen as they are in the other members of 

 this group and they may not be swollen at all, though the genital segments are usually 

 enlarged. The genital pinnules of Chlorometra are very little different from those of 

 Monachometra, of which Chlorometra should perhaps bo regarded as a synonym. Al- 

 though the arrangement of the cirri in Chlorometra appears to be distinctive, it is prob- 

 ably no more distinctive than it is in Chondrometra in which the cirri are arranged in 

 5 midradial columns in C. robusta and C. aculeata, but in 10 columns in C. rugosa. In 

 the other genera the centrodorsal is hemispherical or discoidal with the cirri in irregular 

 marginal rows and only 10 arms. The widely divergent arm bases and small size dis- 

 tinguish Strotometra, while the compressed arm bases of Charitometra are closely ap- 

 pressed and flattened against each other, those of Poecilometra not in contact and more 

 or less concave. 



Of the eight recognized genera of the Charitometridac, five, Chondrometra, Mona- 

 chometra, Chlorometra, Poecilometra, and Strotometra, are, as far as is now known, con- 

 fined to the region between southern Japan and the Lesser Sunda Islands; one, Chari- 

 tometra, is known only from the Kermadec Islands and Fiji; one, Glyptometra, covers 

 the entire range of the family in the Pacific and Indian Oceans, while the closely related 

 Crinometra represents the family in the Caribbean region and at St. Helena. 



