REPORT ON THE CRINOIDEA. 173 
ummit plates be made out. One of the figures’ of the “ perisoma ventrale” in Cyatho- 
erimus alutaceus shows a central plate with seven others round it; while in the other, 
three large plates meet in the centre of the vault, but no one of them could be considered 
as an orocentral. The same may be said of the vault of Cyathocrinus levis represented 
in tab. xxvi. fig. 30. 
As regards the Blastoids I have never been able to trace any definite grouping of 
the summit plates, although I have examined a very large number of picked specimens 
of Pentremites, Granatocrinus, Schizoblastus, and Orophocrinus. 
In Eleacrinus, however, the case is different. There are comparatively fewer plates 
over the peristome, and they certainly often do have a definite grouping, five surrounding 
a central one as was first described by Roemer.’ 
No more need be said about the Blastoids, as their ambulacra are in many ways 
abnormal, though they have strong points of resemblance to those of the Cyathocrinide. 
This family is one of special interest, for Wachsmuth® says that in the structure of their 
vault they “ bear closer resemblance to the recent Crinoids than almost any other group, 
and seem to hold an intermediate position between modern and Paleozoic types. If the 
alternating plates, covering the furrows, could be turned back at the vault by the 
animal, as the Saumplatten of the arms, then the food-groove of these Crinoids was open 
throughout, as in recent forms.” It is possible therefore that although the mouth and 
peristome were subtegminal, 7.e., covered in by the apical dome plates, yet the food- 
grooves of the body may have been just as much external as those of the arms, and in no 
way different from those on the disk of a Pentacrinus. As regards the Cyathocrinide, 
therefore, one of the characters on which Wachsmuth relies as separating the 
Paleeocrinoids from the Neocrinoids would then have no existence, 7.e., the absence of 
external food-grooves. Iam not prepared to assert, however, nor indeed is Wachsmuth, 
that these alternating plates in the radial areas of the vault of Cyathocrinus were 
movable, hike the covering plates of the disk in recent Crinoids. For it seems to me 
quite possible that the closure of the peristome may have been continued outwards on to 
the very short calyx-ambulacra, which would then first become open to the exterior at 
the bases of the arms. But I have no question as to the homology between the radial 
vault pieces in Cyathocrinus, and the covering plates of recent Crinoids, each set passing 
continuously into the covering plates of the brachial ambulacra. 
According to Wachsmuth’s descriptions of the vault of the Actinocrinide the arrange- 
ment of the radial dome plates is the same as that of the radial calyx plates; and he is 
obliged to admit* that the alternating radial dome plates which he finds in Cyathocrinus 
are “not so readily distinguished as in the Platycrinidee and forms with free rays, in 
1 Op. cit., tab. xxiii. figs. 10b, 11. 
2 Monographie der fossilen Crinoideenfamile der Blastoideen und der Gattung Pentatremites im besondern, Archiv 
f. Naturgesch., Jahrg. xvii., Bd. i. pp. 377, 378, Taf. v. figs. 1b, le. 
3 Amer. Journ. Sct. and Arts, vol. xiv. p. 184. 4 Revision, part ii. p. 30. 
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