MONOGRAPH OF THE EXISTING CRINOIDS.' 327 



radials. These lateral fibers have a common poini of origin in the substance of 

 the centrodorsal with the vertical and diverghig fibers around which the calcareous 

 tissue of the basal rays is deposited. It is therefore easy to understand that the 

 calcification may in some cases be so complete that the basal rays formed around 

 the median fibers may become completely united with the walls of the basal grooves 

 formed around the lower ends of the two lateral fibrous masses. The fact that the 

 rays of the basal star are calcifications in connective tissue and not in the ordinary 

 nuclear tissue which forms the organic base of the other parts of the skeleton also 

 affords an explanation of the great variations in the extent to which the rays are 

 developed." 



A single compound basal (figs. 416-422, p. 321), as the structure formed by the 

 union of the basal ray and the intcrradial processes of the rosette has been liappily 

 termed by P. H. Carpenter, consists of two distinct elements; (1) the incompletely 

 metamorphosed embryonic basal, and (2) a single ray of the basal star. "An isolated 

 compound basal which is thus constituted, when seen from its dorsal side, shows 

 (1) more or less of the calcareous network wliich unites the ventral surface of the 

 rosette to the internal faces of the radials; (2) a large intcrradial spout^shaped 

 process; (3) two small radial curved processes extendmg outward from the base of 

 the interradial process and representing the unabsorbed lateral portions of the 

 primary layer forming the embryonic basal plate; (4) the basal bridge, consistmg of 

 two calcareous bars that represent the unabsorbed peripheral margins of the embry- 

 onic basal on which two radials rested; they extend toward one another from the 

 outer ends of the small radial processes until they meet at a point that represents 

 the apex of the embryonic basal, and is situated on the dorsal side of the peripheral 

 end of the interradial process developed from the secondary or ventral layer, which 

 becomes united with the basal bridge; (5) the ray of the basal star which is joined 

 to the uitcrradial process, and to the basal bridge along the line of union of the two 

 primary bars constituting the latter, with one another, and with the secondary intcr- 

 radial process, i. e., the apex of the embryonic basal. The development of tliis ray 

 is quite different from that of either the primary or the secondary portions of the 

 compound basal. It is really a tertiary structure, bemg nothing more than a depo- 

 sition of calcareous material in the substance of the connective tissue of the synos- 

 tosis between the centrodorsal and the radial pentagon; (6) at the sides of the inter- 

 radial process, bounded laterally by the radial process, and externally by the bars 

 of the basal bridge, are two large apertures in each compound basal. Through 

 these apertures pass the secondary basal cords wliich result from the bifurcation of 

 the primary cords proceeding from the angles of the chambered organ. The two 

 secondary cords lie in the depressions on the dorsal surface of the compounil basal 

 between the central ends of its radial and interratlial processes. They then pass 

 outward tlirough the apertures beneath the bars of the basal bridge and enter the 

 adjacent openings on the mternal faces of the two contiguous radials, which con- 

 tribute to form the dorsal interradial furrow occupied by the single fusiform ray 

 of the corresponding basal. The ventral surface of each of these rays of a compound 

 basal is not flat like the dorsal surface, but is occupied by a prominent median ridge, 

 so that the ray is triangular in section. This ridge does not extend quite to the 



