34 Revieivs — Wachsmidh 8^ S2Jringer's Monograph on Crinoids. 



Waclismnth and Springer's own diagrams 16 and 17 on p. 131, and 

 still more from specimens of various species, why a plate, here marked 

 a;, occupying almost exactly the same position with regard to the radials, 

 should be called 'anal' in the former and 'tube-plate' in the latter; 

 or why the plates mai'ked t in their diagrams of Hybocrinus (8 ; x in 

 our Fig. 6) and Foteriocrinus (15; r^n our Fig. 14) should not beheld 

 to form part of the cup, since they abut by their sides on plates that 

 are admittedly cup-plates. Moreover, according to this definition, 

 the posterior interradial of the larval Antedon is an 'anal' so long 

 as it lies between the radials. but a 'tube-plate' so soon as it passes 

 above them (Fig. 10). Position, then, affords no practicable or 

 consistent guide. But the proximal tube-plates rarely possess any 

 other feature not shared by the fixed anals. Therefore the dis- 

 tinction between 'anals' and 'tube-plates' rests on no morphological 

 foundation, and the terms, though convenient for general descriptive 

 purposes, are out of place in an argument as to homologies. And 

 yet, as will be seen, it is for the purpose of such an argument that 

 the imaginary distinction has been emphasized, 



Anals appear in the cup in response to the need for widening the 

 posterior interradius so as to allow room for the rectum internally, 

 and so as to support the anal tube in which the rectum is prolonged 

 exter-nally. We can conceive four ways in which this widening 

 may be effected : (1) by simple widening of plates already in 

 existence, as in Platycrinidas ; (2) by splitting or duplication of 

 plates, as the proximal interbrachial of ActinocrinidEe, which is 

 represented by two plates in the posterior interradius : (3) by 

 intercalation of a fresh plate or line of plates, unrepresented in the 

 other interradii, as, possibly, the large anal by which Hexacrinidte 

 are distinguished from Platycrinidse, and the vertical row of anals 

 in Batocrinidee and Dimerocrinidge (=Thysanocrinid8e, W. & Sp.) ; 

 (4) by the lateral displacement or partial atrophy of adjacent radials, 

 permitting other elements to support the tube, as in Hybocrinus, 

 where the right posterior superradial is pushed aside and the 

 proximal plate of the tube rests on the enlarged r. post, inferradial, 

 which thus becomes a ' radianal ' (Fig. 6). 



Now there is no difficulty in any of these conceptions. The 

 examples just quoted are taken from the present Monograph, and 

 probably would be accepted by anyone competent to judge. The 

 difficulty lies in the application to certain cases, notably to the anal 

 area of the Inadunata. Nearly the whole of the sixteen pages on 

 the anal plates is devoted to a discussion of their evolution in 

 that group. 



Most of the Inadunata, especially those with a large anal tube 

 or sac, as well as many of the Flexibilia Impinnata (=Ichthyo- 

 crinoidea), possess in the anal area of the cup from one to four 

 plates. These are not introduced at haphazard, but bear to one another 

 and to the other cup-plates a definite relation. What the precise- 

 relation is, though agreed upon in some cases, remains an open 

 question in others. I'he fullest development is seen in Foteriocrinus 

 and the immediately allied genera (Fig. 14). Here the anals in 



