MORPHOLOGICAL PART. 127 
of the inferradial, which retained its place between the upper sloping faces 
of two basals, only changing its outlines to conform to the shape of, and fit 
in between, adjoining plates. In the Carboniferous, in which the ventral sac 
attained its greatest dimensions, and the lower faces of the costals frequently 
fill up the whole width of the radials, leaving no space upon their distal faces 
for an attachment of the tube, the superradial, #, was shifted to the right, 
into a position almost directly above the right postero-lateral basal, and 
obliquely against the inferradial A’ (Poteriocrinus, Fig. 2), Finally toward 
the close of the Carboniferous, when the tube was reduced to its primitive 
insignificance, the anal plates gradually disappeared, and the five radials re- 
sumed their normal position as in Hrisocrinus, Stemmatocrinus, and Encrinus. 
This is entirely different from the interpretation of Mr. Bather, who 
reaches the conclusion that the anal plate x was primitively derived from a 
brachial, and that in geological time it passed down from above into the 
dorsal cup. He regards (op. cit., p. 529) “those forms as primitive in which 
the radianal is more of a radial and less of an anal, in which it is not in an 
asymmetrical position but corresponds to the other lower brachial plates. 
Such forms are Jocrinus, Heterocrinus, Ectenocrinus, Anomalocrinus, and Mero- 
crinus. Now in all these forms « is supported by &, and does not touch LF’. 
Obviously then z is not derived from #’, but originates above &, and on its 
left side. By parity of reasoning we assume the next stage to be repre- 
sented in such forms as Hybocrinus (?), Ottawacrinus, Dendrocrinus, and Homo- 
crinus, since in them W&’ is rather more asymmetrical. In these a has 
passed down from above #, and now rests with its lower half between the 
right and left posterior radials, being supported partly by f’ and partly by 
the basal. Carabocrinus, Botryocrinus, and similar forms are, as all acknowl- 
edge, the next stages in the shifting of the radianal; in these z has sunk 
still lower into the dorsal cup, and is now entirely in a line with the radials. 
... In Parisocrinus and Euspirocrinus among pinnuless forms, and in the 
Poteriocrinites, another change has taken place; the radianal has passed 
through a revolution of 90°, and the lowest plate of the ventral sac (¢) has 
sunk down between FR and z.” 
Before inquiring into the validity of this argument, it will be well to ascer- 
tain whether the plates of the different genera which Bather calls 2 are 
structurally the same thing, for an error in this respect would be fatal to the 
whole theory. The question is, is his plate # in Jocrinus and Meroerinus, 
which rests upon the one marked by him FR or C, and that resting upon F’ 
