MORPHOLOGICAL PART. 129 



truncate upper face of plate x. The plate to the right lies at a somewhat 

 higher level than the one to the left, and does not touch x, owing to the 

 greater length of the compound radial, while that to the left touches it 

 slightly. The three plates form part of the free tube, and each one is fol- 

 lowed by a vertical row of other tube plates. 



Comparing this structure with that of Ileterocrinus (Fig. 10), Ectenocrinus 

 (Fig. 11), and Ilyhocrinus (Fig. 8), we find that the plate t in all these forms 

 takes practically the place of the three plates {ttt) in Dendrocrinus. In 

 either case the plates constitute the lower tube plates, and rest — the one 

 as well as the three — upon the sloping upper faces of the two posterior 

 radials- but while the three plates of Dendrocrinus are supported by a special 

 anal plate, the radials of Ileterocrinus, etc., meet underneath, and the anal is 

 unrepresented. In Dendrocrinus, which has an extremely large anal tube, 

 the anal x is well represented ; while in the three other genera, in which the 

 tube is narrow, and the outer edges of the radials are sufficient to support 

 it, that plate is wanting. If it were true that the plate t in Heterocrinm 

 represents the plate x, and sunk down in palaeozoic times to the basals, as 

 supposed by Bather, the plate x would be represented twice in Dendrocrinus 

 Casei, once by x, and again by t, both plates being present and in place. 



Bather makes the statement (p. 331) that the " brachianal " and the 

 plates succeeding it in regular series, are to be regarded as brachials, but 

 that the remaining plates of the sac are nothing more than plates deposited 

 in an extension of the ventral perisome, and in conformity with this he 

 has called the superradial of locrinus an axillary plate. The term '' axillary " 

 in Crinoid terminology is given exclusively to plates of the rays, and every 

 axillary is followed necessarily by a branching of the arm. Bather in using 

 that terra must have supposed that the so-called brachianal, and the plates 

 succeeding it, are parts of a modified arm, which in geological time became 

 incorporated into the sac, for in no other way could we understand why he 

 called it an axillary. He has probably been misled by the angularity which 

 occurs upon the upper face of the superradial, or by the form of the plates 

 succeeding it to the left, and the slanting position of the posterior arm to the 

 right. In that case he overlooked that the radials in Actinocrinus alpo have 

 sloping upper faces, and yet that those plates are not axillaries, supporting 

 as they do at one side a costal, but an interbrachial at the opposite side ; 

 and it did not occur to him that such might be the case also in locrinus. 

 Examining the anal interradius as it appears in the Camerata among the 



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