CALAMOCRINUS DIOMED.E. 23 



Hall figures in the Twenty-fourth Annual Report (18V2) of the State 

 Museum of Natural History of New York, Plate V. Fig. 14, a portion of an 

 arm bearing pinnules, in which the joint carrying the pinnules may justly 

 be considered an axillary ; yet it is only a one-sided joint, as in the case 

 of the joint (the modified axillary) for the first pinnule of Calamocrinus. 



Akm Joints. 



The arm joints are remarkable for the great size of the muscular foss«, 

 and the expansion of the fossa for the dorsal ligament. The transverse 

 ridges separating the muscular fossje from the fossa for the dorsal ligament 

 vary greatly in direction and in .shape. Sometimes it is a straight ridge 

 running obliquely across the joint (Plate XIV. Fig. 4). In other cases the 

 ridge on the two sides of the axial canal runs off at a different angle 

 (Plate XIV. fig. 2), or one shank of the ridge is slightly curved (Plate 



XIV. Fig. 9, Plate XV. Fig. 2), either convex or concave. Or it forms a 

 slightly curved arch, concave towards the dorsal side, for the reception of 

 the dorsal ligament (Plate XIII. Figs. 11, 14, Plate XIV. Figs. 8, 10, Plate 



XV. Fig. 5). 



The arm joints are never symmetrical, one side or the other being uni- 

 versally the largest (Plate XIII. Figs. 11-14, Plate XIV. Figs. 2-5, 8-10, 

 Plate XV. Figs. 1-5), and the largest side is not uniformly the one in which 

 the symmetry is disturbed by the cavity for the insertion of the pinnule 

 (Plate XIII. Figs. 13, 14, Plate XIV. Fig. 3, Plate XV. Fig. 5) ; though such 

 is the case in Plate XIV. Fig. 8 and Plate XV. Fig. 4. 



The transverse ridge may be more or less fiat; sometimes it is quite broad 

 with very indistinctly rounded edges (Plate XIII. Fig. 11), or comparatively 

 narrow with sharp edges (Plate XIV. figs. 3, 4, 9), or quite indistinct towards 

 the edges (Plate XIII. Fig. 14, Plate XIV. Fig. 10). The reticulation of the 

 fossa3 is quite compact, presenting on the surface a delicately pitted ap- 

 pearance. (See Plates XIII., XIV., and XV.) The reticulation is somewhat 

 coarser near the transver.se ridges, and also towards the ventral surface 

 of the joints. The syzygial faces are usually more uniformly pitted (Plate 

 XIII. Fig. 12, Plate XIV. Fig. 5, Plate XV. Figs. 1, 3), and show a radial 

 arrangement of the cells on the periphery of the joints, generally more 

 marked than the similar radiating lines extending in some of the fosste 

 from the outer edge inward (Plate XIII. Figs. 11, 13, Plate XIV. Figs. 2, 4, 

 10, 12, Plate XV. Fig.s. 4, 9, 11, 12). On the outside surface of the arm 



