994 MR. p. A. BATHEB OTf rUSTTACBIIfrS. [Dec. 17, 



epizygals gradually diminish slightly in height, till they become 

 about two-thirds the height of an ordinary brachial, rarely less 

 (PL LIV. fig. 11). It is often very hard to decide whether two 

 adjacent ossicles are united by syzygy or no, so little do they 

 differ in outward appearance from the neighbouring brachials. 

 Occasionally the syzygial joint is a little less curved, as though 

 there were some attempt at dovetailing, a suggestion of the 

 structure in Pentacrinus naresianus and P. blahei. 



The pinnules. — The law of pinnaJation for the fixed pinnules 

 has been discussed fully. That for the free brachials is the same 

 as obtains in most modern crinoids : each ossicle, except the 

 hypozygals, bears a pinnule, and the pinnules are on the right 

 and left sides alternately. Viewed from the side of the arm, as 

 in fig. 11 of PI. LIV., the proximal ossicle of each pinnule appears 

 sub-crescentic in outline, and lies in a corresponding semicircular 

 notch, excavated in the upper corner of its brachial. The lower 

 corner of the succeeding brachial is also shghtly excavated, and 

 the pinnulars fit closely up against it. In the case of a syzygy, 

 the notch for the proximal pinnular may extend a little below the 

 epizygal and include a small portion of the hypozygal. When 

 seen from the back of the pinnule, each pinnular, with the 

 exception of the proximal one, has its upper and lower margin 

 parallel to each other ; but seen from the side each ossicle has a 

 sub-triangular outline, the base of the triangle being dorsal. 

 This is seen to a slight extent in fig. 13 of PI. LIV. In other 

 words, each pinnular decreases in thickness towards the ventral 

 side of the pinnule ; and this enables the pinnule to curl upwards 

 over the ventral groove of the arm. This feature is more marked 

 in the proximal region of the pinnule than in the distal. As is 

 usually the case with both arms and pinnules in the Crinoidea, the 

 proximal ossicles of each pinnule are wider than high, while the 

 distal ones are higher than wide. There are at least 30 ossicles 

 in each pinnide ; in some, 40 can be counted. In some cases the 

 pinnulars show a concavity of the sides like that in the brachials 

 (PL LIV. fig. 13). 



On the ventral side each pinnule has a shallow groove (PL LIV. 

 fig. 14). This was probably roofed by covering-plates, though 

 none are preserved in the fossil. On either side of the groove, 

 and at right angles to it, is a slight depression or channel in each 

 pinnular. These may have been for the passage of the tentacles, 

 or they may represent articidar depressions for the covering-plates 

 such as 1 have figured for Cyathocrinus acinotuhvs and C. ramosus^. 

 The objection to the latter interpretation is that the covering- 

 plates must in that case have been rather too large and solid to 

 have so entirely disappeared. 



The articular surfaces of the pinnulars (PL LIV. fig. 12) appear 

 to show an axial canal separate from the ventral groove, and on 

 either side thereof a depression for attachment of ligament, i. e. a 



1 " Crinoidea of Gotland," i. figs. 208 & 255, in Svensk. Vet.-Akad. Hand). 

 XXV. 2 (1893). 



