

MONOGRAPH OF THE EXISTING CKINOIDS. 115 



centrodorsal the specimen belongs to the Atelecrinidje (fig. 227, p. 245); species 

 of the PentametrocrinidsB have very long and slender arms, a large black sharply 

 stellate disk, a very evident synarthry between (ho first two post-radial ossicles, a 

 hemispherical centrodorsal bearing numerous slender, deciduous, long-jointed, 

 strongly flattened cirri, and very slender, rounded, or flattened pinnules, all of which 

 are approximately the same (figs. 113, p. 181, and 119, p. 185); species of the family 

 Zygometridie have short and comparatively stout arms, a small, light colored, com- 

 pact, and rounded disk, apparently a syzygy (in reality a pseudosyzygy) between the 

 first two post-radial ossicles, a thin discoidulcontrodorsal bearing a single, or at most 

 a partially double, row of short, tenacious, rather stout, usually short-jointed but 

 only slightly flattened cirri, and stout prismatic lower pinnules, which are very 

 different from the slender distal pinnules (figs. S3, p. 136, and 84, p. 137). 



If the arms divide, attention should bo directed to the disk and oral pinnules; 

 if the latter have terminal combs (usually, but not always, correlated with an 

 excentric mouth and a central or subcentral anal tube) the specimen belongs to the 

 ComastericL-e (figs. 25-28, p. 69, 56-58, p. S3, and 59, 60, p. 85). 



If it should prove to possess a central mouth and smooth tipped oral pinnules, 

 then the type of articulation between the two elements of the first division series 

 should be determined ; if they appear to be united by syzygy (in reality by a pseudo- 

 syzygy), the specimen belongs to a species of the family Zygometridse (figs. 37-40, 

 p. 75). 



If, however, they are not united by pseudosyzygy, then the pinnules should be 

 examined ; if all the pinnules are strongly prismatic with their ambulacra bordered 

 by well-developed side and covering plates (figs. 7, p. 63, and 53-55, p. 81), the 

 families Thalassometridse, Charitometridse or Calometridaj are indicated. Species of 

 Calometridas have the division series more or less separated from each other laterally 

 (never flattened against each other), a small globose disk entirely covered with a 

 firm calcareous plating, and comparatively slender, though very stiff, pinnules, of 

 which the earlier have the first two segments (especially the first) greatly enlarged; 

 the first pinnule, moreover, is alwaj's small and very weak, flexible and delicate, 

 eo that the first two segments appear all out of proportion to the rest of the structure; 

 the cirri are always rather long, moderately stout, and are composed of usually short 

 subcqual segments, of which the distal bear dorsal processes (figs. 19, p. 67, and 89, 

 p. 147). Species of Charitometridte have short, very stout, smooth cirri which 

 are composed of subequal segments, rather large pinnules, of which the first two 

 are longer than the succeeding, but more slender and composed of very much 

 more numerous and shorter segments, and the middle are more or less expanded 

 laterally to protect the genital glands; and a disk sunk well within the arm bases 

 and covered with more or less scattered calcareous nodules; the division series and 

 arm bases are strongly flattened against each other and form a closely compacted 

 base (figs. 55, p. 81, 99, p. 160, 100, p. 162, 101, 102, p. 163, and 369, 370, 

 p. 299). The disk and proximal arm structure of the species of Thalasso- 

 metridas is essentially as in those of the CharitometridnB; but the cirri are long, 

 often excessively elongated, comparatively slender, with long segments proximally 

 and very short segments distally, the latter always bearing well-developed dorsal 



