Reviews — Wachsmufh <f' Springer^ s Monograph on Crinoids. 523 



four, Promachocrinus ten, and Gatillocrinus about fifty), but it is 

 not in this sense that Wachsnuitli and Springer say that Techno- 

 crinus spinulostis has "arms twenty," or Batocriims quasillus "arms 

 twenty-two to twenty-four." This confusion would be avoided 

 by using such a word as ramus for the main free branches of 

 an arm. In that case the armlets borne by a ramus might 

 conveniently be called ramuli. 



The account of the arms is remarkably full, and contains many 

 details not to be found elsewhere. Two conclusions of wider 

 interest are arrived at. First, that " the number of costals [i.e. IBr] 

 does not constitute a reliable character for classification, as heretofore 

 supposed, and that in some groups their number is of but little 

 value for specific distinction. This is even more markedly the 

 case with regard to the higher divisions of the rays." The second 

 conclusion is that the fixed brachials of the Camerata " were free in 

 the early larva," " that smaller specimens have a less number 

 of interbrachial plates, that the number increases with the size 

 of the specimens, and that with the increase of the latter additional 

 brachials are incorporated into the calyx." These two conclusions 

 should win ready acceptance by students of Crinoidea. The second 

 is of high importance, for it carries with it the further conclusion 

 that the Camerata were descended from ancestors of Inadunate 

 type, that is, forms with the arras free and distinct, and with 

 the dorsal cup confined to the patina. In other words, if the 

 statement be accepted, it becomes impossible for us to regard 

 such a genus as Beteocrinus, and still more Melocrinus, as truly 

 primitive ; it is not open to us to suppose that any branch of 

 the crinoids was derived from those Cystidea that have a large 

 number of thecal plates ; on the contrary, all the cystidean 

 ancestors of the crinoids must be sought among forms that have 

 their thecal plates limited in number and definite in arrangement. 



We pass now to the plates of the Actinal system (pp. 88-104). 

 Of these the most important are the Orals. At once we are faced by 

 the question : what are the orals ? The only definition that does 

 not admit of controversy appears to be this : The orals are five sub- 

 triangular plates early developed in the interradii around the 

 peristome of the stalked larva of Antedon, but reabsorbed in the 

 adult — and all plates in other crinoids homologous with those five. 

 The disputed point of this definition lies in its application. What 

 plates are homologous ? A full account of the various homologies 

 that have from time to time been maintained by Wachsmuth and 

 Springer and by other writers is given in the Monograph. Additional 

 discoveries have rendered many of these homologies untenable, and 

 what our authors now hold is as follows. 



The orals are represented in Haploci-inus, Pisocrinus, Symhntho- 

 crinus, Allagecrimis, and allied genera (= Larvitbrmia, W. & Sp.) 

 by five subtriangular interradial plates, occupying the whole of 

 the actinal surface, and meeting by their apices around the oral 

 centre. This homology will scarcely find a hostile critic. Five 

 plates similarly situated in the living Rhizocrimts, Hyocrinus, and 

 Molopus have always been accepted as orals. 



