Terms in Crinoid Morphology. 65 
paper, that the anal # descended into the cup from above; and 
I believe that the lowest, median, posterior plate of the ventral 
tube is always this same plate, whether it be right above the 
radials, as in Jocrinus and Merocrinus, resting on the radials, 
as in Heterocrinus and Castocrinus, between the radials but 
not in line with them, as in Homocrinus and Dendrocrinus, 
in line with the radials, as in Botryocrinus and Cyathocrinus, 
or rising above the radials again, as in the later Decado- 
crinidg and in the larval Antedon. In this view I have the 
misfortune to differ from Messrs. Wachsmuth and Springer, 
who apply the term “ anal x ”’ to the lowest plate of the tube 
only when it is partly or entirely within the limits of the 
dorsal cup. They “ apply the term ‘anal plate’ only to those 
taking part in the dorsal cup. All others are plates of the 
anal tube or the ventral sac.’’ That this is not, in their 
opinion, a mere difference of terminology is shown by the 
arguments that they have based on this supposed difference. 
If, however, we consider such a form as Botryocrinus, we 
shall see that the anal # is of exactly the same shape and 
provided with the same axial ridges as the plate that rests 
immediately on it: there is no visible difference between 
them, and whatever the one is that we should suppose the 
other must naturally be. Itis merely for convenience, and to 
distinguish it from the other plates of the cup, that we call 
one of them “ anal x.” 
In exactly the same way, the third anal plate that enters to 
a greater or less extent into the dorsal cup in such genera as 
Dendrocrinus, Poteriocrinus, and Decadocrinus would appear 
to be merely the small plate that in Botryocrinus, Cyatho- 
erinus, and such forms, is seen on the right of anal #, resting 
partly on it and partly on the right posterior radial, and 
corresponding to a similar plate on the left. In other words, 
calling these two plates r¢ and /t respectively, rt is outside the 
cup in Cyathocrinus but partly inside it in Potertocrinus. 
Messrs. Wachsmuth and Springer, however, in their paper 
on the Perisomic Plates (p. 385) have advanced the view, 
apparently for the first time, that in the Poteriocrinites “a 
new plate was introduced beneath the other, a sort of third 
anal.” hat is to say, in their opinion the third anal of 
Poteriocrinus is a fresh development without any homologue 
in the Cyathocrinide and Botryocrinites. But surely the 
constancy in shape and position of the anal cup-plates a and 
rt is hardly consistent with the idea that they are merely 
supplementary plates developed to suit the needs of those 
particular genera in which they appear. It seems more in 
accordance with the principles that have hitherto governed 
Ann. & Mag. N. Hist. Ser. 6. Vol, ix. 5 
