CRINOID GENUS SCYPHOCRINUS 15 



chambers, there being thus as many openings, and as many chambers, as there are 

 ultimate root bifurcations inside the collar. The area within the collar is composed of 

 two sets of plates — one series consisting of larger pieces, fairly regularly arranged, and 

 restricted to the roots that radiate from the stalk ; the other, of irregularly shaped smaller 

 pieces that fill in the spaces between the root radii. The axial canal of the stalk does 

 not pass through the base of the bulb and into the medio-basal chamber, but ends in the 

 primary root member, where it branches and connects with the canals of all the roots. 

 The latter canals pass through all the bifurcations and continue into the outer wall com- 

 municating with the open space between the two parts of the walls. In this way vascular 

 and nervous connection is maintained between all parts of the bulb. [See Schuchert's 

 figures, op. cit, p. 264, text-fig. 43; pi. 41, figs. 1, 3; pi. 42, figs. 3, 4.] 



This description is copied nearly verbatim, and except as to certain points 

 now better understood it is in the main substantially correct; it may now be 

 supplemented by the results of further information. Each pair of roots of the 

 peripheral dichotom within the collar divided further into numerous ramifica- 

 tions which were connected with each other by growth of undifferentiated 

 plates, producing a pair of curving, leaf-like extensions comparable to the con- 

 solidated rays of Crotalocrinus, which progressively met by their edges and 

 fused, forming a short, tubular opening which expanded into an ovoid sac, 

 composed of a single wall. Thus arose a circlet of four or more large sacs, 

 suspended from the edge of the pavement-like area bounded by the collar, and 

 mutually in contact toward the center. A polygonal space was left at the center 

 between the sacs, which is the " medio-basal " chamber of Schuchert, as shown 

 by his figure 4 of plate 42 ; in this there are five sacs, with the openings toward 

 the stalked end away from the observer, not shown in the figure owing to the 

 deep shading. 



Meanwhile other systems of plates derived from the principal root members 

 extended themselves by continuous multiplication in different directions so as 

 to form : ( 1 ) a projecting collar bounding the area occupied by the sac open- 

 ings and the root members leading to them; (2) a connecting pavement between 

 the root members within the collar; and (3) a wall enclosing all the sacs and 

 constituting the outer wall of the bulb as now seen. The last is also a single 

 wall. But wherever it touched the walls of the sacs, or wherever the walls 

 of two sacs came together, there, and only there, do we find a double wall. See 

 Hall's figure 7 of plate 35 of the 28th Report, where in a cross-section the 

 walls of the sacs appear single around the " medio-basal " chamber, and become 

 double in the partitions where those of two sacs meet and where the latter meet 

 the exterior wall. These different walls are not independent structures, but 

 all have a common origin, being derived directly from the ramification and 

 inter-connection of the roots; and they are innervated by a common nervous 

 system. It is probable that the openings leading to the sacs were closed in 

 life by some kind of membranous structure, as no foreign objects are found 

 within the chambers except homogeneous matrix deposited during fossilization. 



