and Anatomy of the Echinodermata. 363 



Crinoidea and Asteroidea are of the same antiquity. Both 

 groups make their appearance as early as in the Silurian 

 formation. But the species which here first come under our 

 notice are such as can by no means pass as primordial forms. 

 These have not been preserved for us. This becomes intelli- 

 gible if we consider that in them the calcareous skeleton, and 

 therefore the parts best adapted for preservation, will have 

 been still but scantily developed, and that in general all the 

 remains of Asterida appear to be very badly preserved, so 

 that they generally occur only in fragments. Hence we 

 cannot expect that palaeontology will ever elucidate the 

 phyletic history of this group. This opinion, which has also 

 iDeen expressed by Zittel (Handb. der Pal. i. 1, p. 309), has 

 not been adopted by other palaeontologists, such as Neumayr*, 

 but they have established a genealogy of the Echinida almost 

 exclusively upon pala?.ontological data. Whether this genea- 

 logy is reconcilable with the anatomical data is a matter 

 which I will briefly discuss. 



According to Neumayr the Cystidea are to be regarded as 

 the stock -group of the Echinodermata, therefore a group 

 which others have united with the Crinoidea, and from them 

 the Crinoidea are supposed to have branched off. This 

 branching off is no further demonstrable, as both groups make 

 their appearance side by side in the Lower Silurian, and 

 earlier remains have not yet been found. The assumption 

 that the Cystidea are the most ancient Echinid group has 

 therefore not even a palseontological foundation. Further, 

 according to Neumayr, the Ophiuroasterida have branched 

 off from the Cystidea, and the Echinida in another direction. 

 Other naturalists have already raised the question whether, if 

 certain forms of Cystidea, such as Agelacrinus, remind us of 

 the Asterida^ this is not due to mere accidental external 

 resemblances. The same applies no doubt to the resem- 

 blances which have been found between Cystidea (such as 

 Mesites) and Echinida. As Homes saysf, the genetic rela- 

 tions here are still very doubtful. 



If we add to this that important objections have been raised 

 against the homologization of the basal plates of the Cri- 

 noidal calyx with the apical plates of the Echinida (H. 

 Carpenter), the probability of the derivation of the Echinida 

 from the Crinoidea is still further diminished. 



To all this must be added, and this gives the finishing 



* " Morphologisclie Studien liber Echinodermeu,'' in Sitzungsb. d. k. 

 Akad. Wiss. in Wieii, Bd. Ixxxvi. (1881). 



t ' Elemente der I'alaontologie/ 1884, p. 173. 



