MOXOURAPU OF THE EXISTING CBINOIDS. 375 



that the inner margin of the dorsal surface of the radials is not notched, but straight, 

 the radial axial furrow not being continued so far toward the dorsal surface as in 

 Antedon; and also that process grows inward from the two sides of the dorsal 

 end of each of the five spoutlikc rays of the rosette, so that the lumen of the canal 

 it encloses becomes much diminished; while in some cases similar processes are 

 put forward from the margin of the radial, which unite with the others so com- 

 pletely as entirely to obliterate the lumen of the radial axial canal, and thus form 

 its dorsal boundary. 



Pits similar to those of Antedon are seen in the species of Cyttometra; but 

 among recent comatulids the most striking development in this respect is seen 

 in such species as Heterometra quinduplicava, H. reynaudii, Himerometra mar' 

 tensi, Craspedometra acuticirra, and in many other of the multibrachiate oligo- 

 phreate forms, as well as in certain large species of Florometra, where the radial 

 axial canals which pass over from the ventral to the inner faces of the radials turn 

 outward again at the bottom of the calyx, and expand into relatively large bilobate 

 or rounded triangular cavities which are formed by excavation in the apposed 

 surfaces of the radials and the centrodorsal respectively (figs. 252-255, p. 253, 

 256-261, p. 255, and 297, p. 263). 



In Asterometra these appear as actual perforations on the ventral surface of 

 the centrodorsal, which reach downward to the bottom of its central cavity as in 

 several fossil species, being only separated from the central cavity by a narrow 

 septum (fig. 268, p. 259). In other species, such as Psathyrometrafragttis, the same 

 condition obtains, but the septum is absent, so that the central cavity, which is 

 naturally decagonal or pentagonal in shape, becomes more or less markedly stellate. 



Where these canals are enclosed by the spoutlike processes of the rosette they 

 are completely shut off, both from one another and from the dorsal extension of 

 the ccelom, which occupies the central funnel-shaped space within the radial pentagon, 

 and passes down into the cavity of the centrodorsal through the central opening 

 of the rosette. On the ventral side of the rosette, however, these radial axial 

 canals are only partially complete, and are in free communication with the numer- 

 ous plexiform spaces into which the funnel-shaped space is broken up by the above- 

 mentined calcareous network. The central portion of this system is very irregular; 

 but peripherally the plexus becomes more regular, and five axial interradial canals, 

 lying in the axial interradial furrows formed by the truncation of the ventrolateral 

 angles of each basal, which, like the axial radial furrows, are partially bridged over 

 by the inosculating calcareous processes which extend themselves toward the 

 ventral aspect of the rosette, are traceable between the five radial ones with which, 

 as with the center of the plexus, they are in free communication. These inter- 

 radial canals are continuous with the interradial furrows which are visible on the 

 ventral aspect of the radial pentagon, and they inclose diverticula of the circum- 

 visceral ccelom to which the name interradial ccelom has been given. They do 

 not descend so far toward the dorsal surface as the axial radial canals, and are 

 not, like the latter, enclosed (normally at any rate) by spoutlikc processes of the 

 rosette, for their course toward the dorsal surface is terminated by the five short 



