REPORT ON THE CRINOIDEA. 173 



ummit plates be made out. One of the figures^ of the "perisoma ventrale " in Cyatlio- 

 crinus 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 IcBvis represented 

 in tab. xxvi. fig. 36. 



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 difi"ereut. 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 Cyathocrinidse. 

 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 Palaeozoic 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, i.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 difi"erent from those on the disk of a Pentacrinus. As regards the Cyathocrinidfe, 

 therefore, one of the characters on w^hich Wachsmuth relies as separating the 

 Palseocrinoids from the Neocrinoids would then have no existence, i.e., the absence of 

 external food-grooves. I am not prepared to assert, however, nor indeed is Wachsmuth, 

 that these alternating plates in the radial areas of the vault of Cyathocrinus were 

 movable, like 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 Actinocrinidse 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 PlatycrinidjB and forms with free rays, in 



1 Op. cit, tab. xxiii. figs. 10 J, 11. 



2 Monographie derfossilen Crinoideenfamile der Blastoideen undder Gattung Pentatreinites im besondern, Archiv 

 f. Naturgesch., Jahrg. xvii., Bd. i. pp. 377, 378, Taf. v. figs. \h, \c. 



3 Amer. Journ. Sci. and Arts, vol. xiv. p. 184. * Revision, part ii. p. 30. 



