REPORT ON THE CRINOIDEA. 47 



IV.— THE RAYS. 



A. The Eay-divisions and Arms. 



The arms of a NeocrinoicI, viewed in a strictly morphological aspect, must be regarded 

 as commencing with the first joints beyond the primary radials. The same is the case in 

 many Palseocrinoids, of which Schultze says, " Die Arme (brachia) beginnen unveritn- 

 derlich da, wo eine deutliche Gelenkfacette eines festen Kelchstiickes ihren Ursprung 

 anzeigt."^ In the Platycriuidas and other Palaeocrinoids, and in all Neocrinoids (except- 

 ing perhaps Guettardicrinus), this articular face is on the first radial. In the five-armed 

 Eudiocrinus indivisus the next joints beyond the radials are syzygial, with pinnules on 

 the epizygals,^ which clearly shows that they must be considered as arm-joints and not as 

 belonging to the calyx, although they undoubtedly represent the so-called second and 

 third radials of a ten-armed Crinoid. The other species of Eudiocrinus have these two 

 primitively separate joints not united by syzygy but articulated, just as in Hicmmatocrinus 

 (PI. LVI. figs. 1-4). The second one bears a pinnule both in Thamnatocrinus and in 

 Eudiocrinus varians ; but in Eudiocrinus semper i n,ni\. Eudiocrinus jajwnictis the &Tst 

 pinnule is on the fourth joint after the radial. This would correspond to the second 

 brachial of a ten-armed Crinoid, but it is really the fourth brachial in Eudiocnnus. 

 Lastly, in Perrier's Eudiocrinus atlanticus ^ the first pinnule is on the fifth brachial, which 

 corresponds to the third brachial of an Antedon. 



The well-known genus Rhizocrinus resembles Eudiocrinus indivisus in the syzygial 

 union of the first two joints beyond the primary radials (PL X. figs. 1, 2, 6-8, 20). 

 They have generally been called the second and third radials ; and there is some ground 

 for this in the case of Rhizocrinus lofotensis, as they are considerably broader than aU the 

 joints which follow them except the first (PI. IX. figs. 1,2). But in Rhizocrinus rawsoni 

 (PI. IX. fig. 3 ; PI. LIII. fig. 7) they are not much larger than the four following joints, which 

 contribute with them to support the visceral mass (PI. X. fig. 20) ; while the first pinnule 

 is on the last of these, i.e., on the sixth joint above the cal}-x (PI. IX. fig. 3 ; PI. X. fig. 20). 

 Considering the evidence afi'orded by Eudiocrinus, I think, however, that it will be more 

 consistent to describe Rhizocrinus as having only one radial; while the first pinnule 

 would then be on the sixth {Rhizocrinus raivsoni) or on the eighth brachial {Rhizocrinus 

 lofotensis). The terms second and third radials would then be used only in those cases 

 where there are ten or more arms, owing to the thii-d radials and more or fewer of the 



1 Op. cit, p. 5. See also the genus Actinometra, Trans. Linn. Soc. Land. (Zool.), ser. 2, vol. ii. pp. 20-25, 1883 ; Zittel's 

 Palc-eontologie, t. i. p. 339; de Loriol, Paleont. Frang. Terr. Jurass., t. xi. p. 15; Wacbsmuth, Revision, part ii. pp. 9, Irt. 



2 Eudiocrinus and Atelecrinus, Journ. Linn. Soc. (Zool.), vol. xvi. p. 495, 1882. 



3 Sur des Eudiocrinus de I'Atlantique et sur la nature de la faune des grandes prol'ondeurs, Covvjtes Rendus, t 

 xcvi. No. 11, p. 726. 



