402 SMITHSONIAN INSTITUTION 



the food-groove, or perhaps solely for support. The smooth and rounded right margin of 

 the part of this ray below the axillary is shown in figure 6d; the proximal articulating face 

 of the radial in 6e ; and the distal face of the second primibrach above it at 6/. These views 

 of the articulating faces, together with those shown by figures ya-h from detached brachials 

 in a similar specimen up to the axillary IIIBr, show the great depth and massiveness of the 

 Taxocrinoid ray, as compared with that of Forbes'wcrinus. 



Returning to the posterior basal, — in figure 4 it is fully exposed free from the tube 

 plates, showing the relatively low position of the socket, the strongly rounded distal margin 

 connecting by an even curvature with the smooth margins of the posterior rays, and the 

 complete absence of any face for sutural connection, either upon this plate or those to the 

 right and left of it. All this is further emphasized by figures 8a, b, where we have a well- 

 preserved calyx entirely freed from the matrix dorsally and ventrally ; 8b shows the same 

 view of the posterior basal, and the curved margins of the adjoining rays ; and 8a the inner 

 edge of these margins connecting in a gentle curve with that of the posterior basal, all per- 

 fectly rounded and free from any sutural connection. These figures show that the posterior 

 basal is sometimes really more symmetrical than it appears ; the leaning of the tube to the right, 

 or the apparently greater excavation of the right shoulder, being often partly the result of 

 pressure in fossilization. Figures 8a, b bring out clearly the next important point in typical 

 Taxocrinus, viz. : 



(2) The Interbrachials. These instead of running upward to an apex between the ray 

 divisions have a more or less curved and crescentic distal margin marking the limit of solid, 

 suturally connected plates, and the beginning of pliant perisome ; the margin is smoothly 

 rounded, and the perisome attached at its inner edge, as is finely shown in figure 3a. 



The various stages of the arcuate sutures between brachials, which gave rise to the 

 notion of " patelloid plates," are thoroughly illustrated on the same plate ; the ordinary form — 

 broad median curvature of the exterior suture line — is seen in such specimens as figures 2, 

 3, 4, 5 ; the extreme form, where the projecting lips from the proximal faces look as if cut 

 off by transverse lines into separate plates, in figure 1. Figure 9 shows that the external 

 appearance depends purely on the condition of preservation of the surface, this being a 

 weathered specimen in some parts of which the sinuous suture lines are plainly visible, while 

 in others they have been obliterated by erosion, leaving the sutures as they actually are just 

 below the surface, viz., straight lines. The detailed structure of this may be seen in figures 

 6a, b and Ja, b, in the latter of which the projecting lip, and the corresponding indentation 

 fitting it on the plate below, are drawn from the separated plates ; and the suture line, exteriorly 

 arcuate on the face of IBr 2 in 6a, is seen to be perfectly straight at the ventral side in 6b. 



Among the numerous specimens of this species some interesting special cases have been 

 observed. Among these are — 



(3) Malformation. This is shown by figures 10a, b, c of Plate LVII, where the speci- 

 men has apparently six rays, the left posterior radial being an axillary and supporting two 

 equal series of primibrachs ; there is accompanying confusion among the basals, only four of 

 them being in the ring, while the fifth is superimposed at the posterior side, as shown in the 

 diagram. Still more interesting than this is a remarkable case of — 



(4) Recuperation (PI. LVI, figs, no, b, c). In this case the entire crown except the 

 infrabasals and one basal has been broken off and replaced by new growth ; the stem and 

 plates mentioned clearly belong to a much larger crinoid, and the one remaining basal tells 

 very plainly what has happened. Here also are six rays, one directly following the old basal 

 without any regard to its angular axillary face which remains exposed exteriorly ; one oppo- 

 site to it, and two each from axillary radials at either side ; three greatly unequal new basals 

 are developed beneath these. This individual had only one basal left to build upon, and the 

 recuperation of the entire crown from this indicates that the seat of vitality was lodged low 



