26 CALAMOCRINUS DIOMED.E. 



radiating lines is fully as prominent as in the pinnule joints in Plate XVI. 

 Figs. 8, 12. With the exception of the lower stout pinnule joints of those 

 which are ijlaced near the base of the arras adjoining the calyx, they have 

 no distinct articulating face. There is a broad ridge with rounded edge, 

 through which passes the axial canal of the pinnule, and which corresponds 

 in a general way to the transverse ridge se):)arating the dorsal ligament 

 from the muscular fossas. But there are no well defined fossjB, the ridue 

 forming with the adjacent joint a sort of rudimentary ball and socket joint 

 (Plate XIII. Fig. I), while in more distal pinnule joints the articulating 

 faces are nearly flat surfaces (Plate XIII. Fig. 2, and Plate XVI. Fig. 7), 

 even, as in the last case, where the buttresses of the sides of the pinnules 

 have undergone considerable development. 



The development of the lateral wings of the pinnule joints appears to 

 be quite irregular, especially in those pinnules which are near the base 

 of the arms attached more or less to the surface of the disk, the size of 

 the wing depending greatly upon the freedom for expansion which it meets ; 

 so that it is not an uncommon feature to find the wing of one side greatly 

 developed while that of the other is quite narrow or absent. Compare Plate 

 XVI. Figs. 6, 9-13. The reticulation of the limestone meshwork of the 

 pinnule joint is comparatively coarse, much as is the case with the reticu- 

 lation of young arm joints. See Plate XVI. Figs. 14-17. 



According to the position of the pinnule joint, the degree of development 

 of its lateral wings, and the number of its dorsal sjjines, the articulating 

 face varies between that given in Plate XVI. Fig. 7, and that figured in 

 Plate XIII. Fig. 2. 



As has been noted before, the arrangement of the primary pinnules of 

 Calamocrinus is somewhat different from that of the majority of Crinoids, 

 whicli have the third radial an axillary, and in which the joint preceding 

 the axillary bears no pinnule.* There is of course no pinnule at the axillary, 

 and the first joint after the axillary carries no pinnule, as in the majority 

 of the Comatulte and some species of Pentacrinus. 



We note the same differences in the lowest pinnules of Calamocrinus 

 which characterize those of the Comatuloe, of Pentacrinus and Metacrinus ; 

 their basal joints are ornamented with spurs and Iveels, and the shape of 

 the joint is rectangular. 



* In Metaciirms there is a pinnule below the axillary. Chall. Rep., Plate XXXVIII., and Plate 

 XLIII. Fiff. ■-'. 



