KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 25. N:0 2. 59 



curved articular facet, on either side of which are slight radial processes: the true articular 

 nature of these faeets is eonrirmed by examination of the corresponding plates in other 

 genera (Ringueberg, op. cit., Pl. X, ng. 13 a}. There are two plates, rather larger than 

 the others, form ing what may, loosely speaking, be called the sides of the cup: eabh of 

 these is a complete radial. In the single radius that intervenes between these large ra- 

 dials, there are two plates, which are regarded as the upper and lower halves of another 

 radial by Wachsmuth and Springer and W. R. Billings; other writers also have considered 

 both plates as elements of the dorsal cup; Ringueberg alone has referred the second plate 

 to the brachial series. Euchirocrinus and Calceocrinus afford no evidence in support ©* 

 Ringuebergs view; he has doubtless been led to it by the fact that in Castocrinus fur- 

 cillatus, C. rugosus, C. Billingsianus and perhaps in other species, the distal plate is slightly 

 more raised above the general margin of the cup and appears to be attached to the 

 proximal plate bv an articulation. If this be Dr. Ringueberg's argument, there is much 

 force in it; but the following considerations incline me to abide for the present by the 

 old view. The presence of an articulation between the two plates does not necessarily 

 make the distal one a brachial, for there is in this family an articulation between basals 

 and radials: this articulation has not been absolutely proved, it disappears in subsequent 

 genera, and never has that characteristic appearance, with processes on either side, that is 

 possessed by the articulation betAveen the distal plate and the ensuing brachial in at least 

 some species of Euchirocrinus and Calceocrinus: fmally, in the type-specimen of Casto- 

 crinus rugosus, in which the joint surface of the proximal of the two plates is exposed, 

 I can detect no trace of an articulation. The sinking of a brachial into the cup, which 

 follows from Dr. Ringueberg's hypothesis seems less in accordance with the general evo- 

 lution of this genus, than the gradual diminution of the two halves of a radial: and were 

 the distal plate a brachial in Castocrinus, we should expect it to be pushed out of the 

 cup, by the meeting of the larger radials, in låter genera; whereas the contrary is the case, 

 for there is of course no room for doubt but that the distal plate in Castocrinus repre- 

 sents the distal plate in Calceocrinus. We shall therefore be justified in continuing to 

 regard these two plates as the two halves of a radial. On the other side of the cup two 

 radii intervene between the large radials, and in this case too there does not seem much 

 doubt but that in eacli the radial is compound : the transverse sutures are not, as usual, 

 horizontal, but are oblique, so that the proximal portions of the radials are a little pushed 

 away from one another; this however is clearly connected with the bending över of the 

 crown on this side. The distal halves were regarded by Dr. Ringueberg as brachials, 

 and in this I inconsiderately followed him 1 ): on niature reflection however, and after 

 examining 7 specimens of Castocrinus, I prefer to return to the view of Mr. W. R. Bil- 

 lings in his original description of that species 2 ); my chief reasons for this are the 

 absence of any articulation between these plates and the proximal portions, and the pre- 

 sence of a well-marked articulation, with traces of radial processes, between them and 

 the ensuing plates. 



*) »The Classification of the Inadunata Fistulata. •> Ann. Mag. Nat. Hist., 6 ser., vol. v, p. 330, Pl. xxiv, 

 fig. 9, April, 1890. 



2 ) Ottawa Naturalist, vol. I, no. iv, p. 51, July, 1887. 



