22 CALAMOCRINUS DIOMED.E. 



adjoining brachials united by syzygies or trifascial articulations, and carry- 

 ing no pinnules; while if we consider a brachial to be represented by each 

 face, the first pinnule appears on the sixth arm joint in Hyocrinus, the 

 first axillary on the third in Bathycrinus, and the first pinnule on the 

 eighth in Rhizocrinus and on the fourth in Calamocrinus. 



While in Metacrinus the first pinnule is on the second brachial or the 

 third joint, the first axillary in almost all Neocrinoids is, according to Car- 

 penter, the third brachial, with the exception of Metacrinus.* To this we 

 must add Calamocrinus, which differs from Apiocrinus and Millericrinus in 

 having so many radials before the first axillary. It however resembles 

 Metacrinus in having several radials, with a syzj^gy in the second radial. t 

 In Guettardicrinus, Apiocrinus, Millericrinus, and Encrinus, the arms branch 

 at the third radial, while in Boiirgueticrinus and Rhizocrinus there are five 

 simple arms. 



As has been noticed by previous writers, the joints which carry pinnules 

 really resemble abnormal axillaries; so that if we attempt to use the pres- 

 ence of an axillary at the third brachial as one of the distinguishing fea- 

 tures of Neocrinoids when compared to Palteocrinoids, as has been done 

 by Carpenter, we shall find that there are quite a number of exceptions 

 to the rule. The close resemblance of the joint bearing the first pinnule 

 in Calamocrinus to an axillary is well seen in Plate III. Fig. 6, showing 

 the outline of that side of the joint (the third brachial) to which the first 

 pinnule, pi', is inserted. See also Plate III. Fig. 8, showing the second pin- 

 nule, />?/', inserted to the epizygial of the fourth brachial, which has all the 

 appearance also of an axillary. 



A still more striking illustration of the same point is shown in a some- 

 what magnified figure of the skeleton of the lower part of an arm seen 

 from the interior (Plate XX. Fig. 2), which shows the base of attachment 

 of the first pinnule, pn' , to the third brachial, and that of the second pin- 

 nule to the fifth brachial. 



* AVhile, as has been stated by Carpenter of Neocrinoids with divided rays, in the greater number 

 the thii-d primary radial is the axillary, in Palreozoic Crinoids this is not fixed, and the first radial may 

 be the axillary, and its position is the only distinguishing character of importance between some 

 PaltBozoic genera and Encrinus. 



t In Metacrinus angulatus (Chall. Rep., Plate XXXTX. Fig. 1) the third and fourth radials have 

 pinnules, the fifth being the axillary. In Metacrinus nodosus (Chall. Rep., Plate L. Fig. 1) there are 

 eight radials with syzygies on the second, third, sixth, and seventh joints, all of which have pin- 

 nules except the first and sixth. As Carpenter has remarked (Chall. Rep., p. 52), the position of the 

 brachial syzygies is by no means constant, though of some value among the Comatulse for systematic 

 purposes. 



