,CALAMOCKINUS DIOMED.K 53 



of the disk found on the upper face ol' the top stem joint its outer edge 

 does not reach as yet to the point where new stem joints arise, and is 

 not attached to the hniestone nieshwork of the top stem joint, as is the 

 case with the young stem joints which originate between two okler ones. 

 See Plate XXIII. Fig. 3, and PLite XXI Y. Fig. 7. 



The structure of the joints following the top stem joint is markedly 

 different from it. The distal face (Plate XXI. Fig. 6) of the sixth joint 

 below the top stem joint shows stout short radiating lines only on the 

 outer edge, such as we find in the periphery of all the stem joints, forming 

 a more or less marked milled edge. On the outer quarter of the surface 

 there are a number of stout radiating ridges, from four to five, between 

 a second inner set of fourteen radiating ridges, more or less comma-shaped, 

 which extend to the outer line of the open nieshwork surrounding the 

 axial column (Plate XXI. Fig. 6). The proximal face of the same joint 

 (Fig. 7) corresponds in its structure to the distal face ; the primary radiat- 

 ing ridges, however, are replaced by a corresponding number of sockets. 



In the distal and proximal faces of the ninth joint (Plate XXI. Figs. 8, 9), 

 the arrangement of the reticulation in radiating lines on the outer part 

 of the fiices of the joint, between the sockets and corresponding ridges, 

 is well indicated. In these joints there are sixteen primary ridges (Fig. 8) 

 bifurcating near the edge, and the opposite face shows the corresponding 

 .sockets which fit to the distal f\ice of the eighth joint. This proximal 

 face .shows the sunken lobes upon which may rest a new stem joint 

 similar to the 3'oung joint (Fig. 5), with sixteen lobes formed between 

 the eighth and ninth joints. 



In the upper part of the stem in which w-e find ribbed joints like those 

 of Plate XXII. Figs. 1 and 2, the primary radiating ridges are from six- 

 teen to eighteen in number. They are flattened, leaving large triangular 

 depressions between them (Figs. 3, 4) ; the broad areas being sunken in 

 the proximal faces (Fig. 3), and raised in the distal faces (Fig. 4). Young 

 stem joints lying between the ribbed joints and the flattened joints, such 

 as those of Figure 2, in which the outer lobes find their way to the sur- 

 face of the column, are .shown in Figure 5, which represents a segment 

 of one of these young joints adjoining the distal face (Fig. 4). A seg- 

 ment of a similar, but younger, intercalated joint, which has not yet lost 

 its lobular outline, is represented in Figure 6. The pas.sage of the reticu- 

 lation on the faces of the joints, from the compact ridges of Figure 4 to a 



