326 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Among the Macrophreata the rosette is typically approximately on the same 

 level as the dorsal surface of the radial pentagon. It is thin and delicate, with long 

 and slender rays of which the interradial are but narrow bands or triangular processes 

 of calcareous tissue, though the radial may have their edges more or less everted. 

 In the Pentametrocrinidse it is especially reduced and is very delicate, more so than 

 in any other group. In Coccometra, Compsometra and Antedon, and especially in 

 Heliometra and Florometra, it shows more or less approach to the form seen among 

 the species of Himerometridse or Mariametridse, and may also be more or less sunken 

 below the level of the dorsal surface of the radial pentagon. In Psathyrometra I 

 was not able to find any rosette at all; but I had only a single specimen available 

 for dissection, and the rosette may have been loosened by the alkali by which the 

 skeletal elements were separated and have fallen out. 



In many forms the interradial furrows on the dorsal side of the radial pentagon 

 are very highly developed, and are occupied by five long processes which radiate 

 outward from the angles of the central cavity in which the rosette lies, forming what 

 are known as basal rays. 



Speaking of these P. H. Carpenter says: "In Antedon bifida the edge which sep- 

 arates the lateral and dorsal faces of each radial is tolerably sharp and straight; but 

 in other species, as in Comatula Solaris, it is somewhat truncated, so that when the 

 lateral faces of two radials are in apposition a deep interradial furrow appears along 

 the line of union of their dorsal surfaces, which is continued toward the dorsal or 

 outer surface from the central or inner aspect of the pentagonal base." 



The basal rays are formed by the more or less complete calcification of the cen- 

 tral portions of the great mass of fibrous tissue developed along the interradial por- 

 tions of the centrodorsal and of the pentagonal base of the calyx, which lie within 

 these furrows. 



Carpenter says: "At the proximal end of the basal ray are two openings, one 

 on either side, which give passage to the secondary basal cords; and they are sep- 

 arated when seen from the dorsal side by the interradial process of the rosette with 

 portions of the basal ridge. The lateral boundaries of these openings are formed by 

 the halves of two of the radial spouts of the rosette which extend outward from the 

 base of the interradial process and represent the unabsorbed lateral portions of the 

 primary layer forming the embryonic basal plate. The ventral side of the basal 

 ray in NeocomateUa alata, Co'mactinia meridionalis, Comatula rotalaria, and in many 

 other oligophreate species, is marked by a relatively large depression which forms 

 the central end of the axial interradial canal. This descends into the calyx over 

 the apposed lateral edges of two radials. But in most cases it ends blindly without 

 reaching the dorsal surface of the radial pentagon at all." 



The origin of the basal ray, which is formed by a more or less complete calci- 

 fication of the central portion of the highly developed interradial masses of fibrous 

 tissue, " accounts for the fact * * * that there is no pigment in the substance 

 of the rays of the basal star * * * nor in the walls of the basal grooves on the 

 centrodorsal, nor in those of the. dorsal interradial furrows on the inferior surface of 

 the pentagonal base, which are calcifications of the smaller lateral masses of long 

 fibers running directly from the organic basis of the centrodorsal into that of the 



