C \I.AM(»ci;iN I S DIOMED I 53 



of the disk found on the upper face of the top stem joinl its outer edge 

 does n<>t reach as yel to the point where new stem joints arise, and is 

 not attached to the limestone meshwork of the top stem joint, as is the 

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

 See Plate XXIII. Fig. 3, and Plate XXIV. Fig. 7. 



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

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

 below the top stem joinl shows stoul 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 <>i the surface 

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

 a second inn t -et of fourteen radiating ridges, more or less comma-shaped, 

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

 axial column (Plate XXI. Fie-. G). The proximal lace of the same joint 

 (Fig. 7) corresponds in its structure to the distal lace: the primary radiat- 

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



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 faces 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 face of the eighth joint. This proximal 

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

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

 the eighth and ninth joints. 



In the upper part of the stem in which we find ribbed joints like those 

 of Plate XXII. Figs. 1 ami 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 passage of the reticu- 

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



