322 Mr. F. A. Bather on British Fossil On no ids. 



radial of Dendrocrinus : he regards it "as a modified radial, 

 the arm-bearing portion of which has been cut off," and he 

 names it the " azygos " plate. In Iloplocrinus too he thinks 

 that " the azygos plate is fundamentally a modified radial 

 belonging to the right posterior ray," though here " that the 

 anal [x] and azygos [R + ] plates may have fused is pos- 

 sible enough." 



In 1883 Messrs. Wachsmuth and Springer continued the 

 discussion in a paper " on Hybocrinus, Hoplocrinus, and 

 Baerocrinus " (Amer. Journ. xxvi. 365-377, Newhaven, 

 Nov. 1883), where they laid the foundation of their present 

 views. In this paper they accepted P. H. Carpenter's homo- 

 logy of the large " anal" plate of Hybocrinus with the lower 

 half of the radial in Dendrocrinus (R + ), and they adopted 

 for it his term " azygos." At the same time, whether in 

 consequence of Carpenter's criticism or not, they executed a 

 complete volte-face on the subject of Iocrinus. They curi- 

 ously misquote Carpenter as having suggested that the 

 axillary plate of Iocrinus was an " azygos " plate, whereas 

 he distinctly admitted it to be a " brachial/' i. e. costal. 

 Instead they " insist that it is the equivalent of the combined 

 small radial [R] and small anal plate [ x ] in Hybocrinus, 

 and that the large plate underneath, which both Carpenter 

 and [Wachsmuth and Springer] took to be a radial, is an 

 azygos plate." They now take Baerocrinus (PI. XIV. fig. 4) 

 as starting-point, and regard it as having only four radials 

 and " a large undivided azygous plate of similar form." 

 This plate Carpenter had regarded as a radial ; but Wach- 

 smuth and Springer consider that the plate which in other 

 genera represents the right posterior radial is not here deve- 

 loped. In Hoplocrinus the right posterior radial is again 

 developed (PI. XIV. fig. 2) ; it gradually absorbs the right 

 upper corner of the " azygos " plate (PI. XIV. fig. 1), until, 

 in Hybocrinus, it attains somewhat more the shape of an 

 ordinary radial (PI. XIV. fig. 3). In Hybocrinus "the 

 upper left corner of the azygous plate has become divided off 

 into a special anal plate." Iocrinus (fig. 5), Dendrocrinus 

 (fig. 15), Homocrinus (fig. 16), and Botryocrinus (fig. 30) 

 are regarded as a series in which " the posterior radial grows 

 larger by absorbing more and more the azygous plate," until 

 in Cyathocrinus (fig. 20) it has disappeared. In this paper 

 then the authors consider the " azygos " plate to be an inde- 

 pendent morphological element of the dorsal cup, not a modi- 

 fied radial ; e. g. the two plates in the right posterior radius 

 of Dendrocrinus do not represent a compound radial : and 

 they have given up the idea that the ventral sac is developed 



