Retieivs — Wciclismuth ^' Springer's Monograph on Crinoids. 119 



they arose in different branches at different times. Whereas the 

 Melocrinidse {sensn W. & Sp.) existed already in Lower Ordovician 

 times, the rise of the Platycrinidee is traceable in the Middle 

 and Upper Silurian, at which time also the Grotalocrinidfe, which 

 " represent a different degree of departure from the Inadunate 

 plan " (p. 164), first made their appearance. The question that con- 

 fronts us here, as in other Classes of living beings, is whether 

 similarity of modification is to have more classificatory weight than 

 admitted differences of descent. From the day when the cetaceans 

 were first separated from the fish, there has been an increasing 

 tendency to answer this question in the negative, no matter when 

 or where it comes up for solution. 



Even Wachsmuth and Springer admit the heterogeneous nature of 

 their Camerata, and divide the Order into : a Typical Section, in 

 which the lower brachials and interradials form an important part of 

 the dorsal cup ; and a Non-typical Section, in which the brachials 

 retain the form and small size of arm-plates, and the interradials are 

 almost exclusively confined to the tegmen. Had the ' Non-typical ' 

 genera arisen first, and had their non-'typical nature been due merely 

 to arrest of development, there might be some reason or some 

 advantage in associating them with the ' typicals.' But the fact to 

 be emphasized is that they have no connection whatever with the rest 

 of the Camerata. Moreover, they are themselves a heterogeneous 

 lot, for the Crotalocrinidae admittedly have more to do with the 

 Dicyclic Inadunata, (more particularly, the Cyathocrinidee) than with 

 the Monocyclic Platycrinus and its allies. If these statements 

 represent a general opinion, there seems no reason why the 

 Crotalocrinidee should not remain in the Cyathocrinoid division 

 of Dicyclic Inadunata, and why the rest of the ' Non-typical 

 Camerata' should not form an independent Order (of Mouocyclica). 

 For such an Order the name Adunata is elsewhere proposed.^ 



As for the Typical Camerata, they do indeed appear to form 

 a fairly homogeneous group ; but the appearance may be deceptive. 

 Wachsmuth and Springer do not attempt to name any subordinal 

 divisions, but in their analysis (p. 170) they group the families 

 under two main heads : A. Interradials ill defined ; B. Interradials 

 well defined. The former contains both monocyclic and dicyclic forms, 

 all of which are lumped in one family — Reteocrinidge. Group B. 

 undergoes further division into : 1. Monocyclic (Thysanocrinidae, 

 Ehodocrinid^) ; 2. Dicyclic (MelocrinidEe, Calyptocrinidse, Bato- 

 crinidae, Actinocrinid^). Surely it is plain that the " unique and 

 remarkable " structure of the interbrachial areas of the Reteocrinidae 

 represents a primitive stage in the evolution of interbrachials. 

 Their irregular size is supposed by the authors to be due to " the 

 intercalation of supplementary pieces " around the larger plates 

 which "repi'esent" "the first and second row of interbrachials in 

 the Actinocrinidas" (p. 184:). This implies that the structure of the 



^ F. A. Bather, " A Phylogenetic Classification of the Pelmatozoa " : Rep. Brit. 

 Assoc, for 1898, pp. 916-9^3 ; 1899. 



