524 Revieios — Wachsniuth ^ Springer's Monograph on Crinoids. 



In a unique specimen of Taxocrinus intermedins, described by 

 "Wacbsrauth and Springer in 1889, tbere are interradiallj disposed 

 around tbe open nioutb. " five rounded or very obtusely polygonal 

 plates ratber oval in outline," tbe posterior of tbese being " nearly 

 tiiree times as large as any of tbe others " ; tbe food-grooves pass to 

 tbe moutb between tbese plates, wbicb " represent morpbologically 

 the five orals of the recent genera." In the absence of further 

 evidence, we may accept this conclusion provisionally, and we may 

 infer that such was the structure of tbe tegmen in allied genera 

 (viz. in Flexibilia Impinnata). 



In Coccocrinus and Culicocrinus, which are regarded as primitive 

 forms of the ' non-typical Camerata ' (i.e. Platycrinoidea), the greater 

 part of the tegmen is occupied by five interradially disposed plates, 

 which, very naturally, are taken to be orals. In those Platycrinoidea 

 which bave a more complicated tegmen, these five plates can still be 

 recognized ; but in many species the posterior oral has been shifted 

 towards the oral centre by the development of the anal tube behind 

 it, and bas increased in size while becoming partly surrounded by the 

 four remaining orals. In other words, the so-called 'central plate' 

 of the Platijcrinus tegmen is bomologized with tbe posterior oral, 

 while the four so-called ' pi'oximals ' are bomologized with the 

 antero-lateral and postero-lateral orals. There seems no reason to 

 doubt tbe justice of this conclusion. Turning to the ' typical 

 section ' of tbe Camerata, we find a similar ' central plate ' and 

 ' proximals ' developed in many genera, as well exemplified in 

 Actinocrinus ; comparison of these with the structures already 

 described " leaves no room for doubt that tbese are likewise true 

 orals." Here, however, a conscientious critic is bound to point out 

 that external similarity between structures in highly specialized 

 genera is often deceptive and, in tbe absence of genetic affinity or of 

 a plain evolutionary series, cannot be regarded as proof of homology. 

 With such splendid material in their hands, it is a pity that Messrs. 

 Wachsmuth and Springer did not attempt the solution of the problem 

 by a method more satisfactory than that of simple inspection. Tbe 

 task remains for others. It may, however, be conceded that the 

 Camerate tegmen contains no other plates capable of being 

 bomologized with tbe orals. 



Tbere remain for consideration various Inadunate genera 

 (Fistulata, W. & Sp.) of which Cyathocrinus is taken by 

 Wachsmuth and Springer as the type. In this genus are two 

 distinct sets of plates on tbe actinal surface, either set conceivable 

 as homologous with orals. There are five subtriangular plates 

 (deltoids, F. A. B.) resting on .the shoulders of tbe radials, 

 surrounding tbe pentagonal peristome, and meeting by their sides 

 underneath the food-grooves ; the posterior of tbese is tbe largest, 

 and is pierced by water-pores. Again, there are in some individuals 

 five plates (proximals they may be called) interradially disposed, 

 and covering over the peristome ; these plates ai*e continuous with 

 the ambulacrals, often are barely distinguishable therefrom, and often 

 appear absent ; these plates and the ambulacrals, as well as any 

 mmute supplementary plates that may be developed in the tegmen, 



