SALEXIA VARISPINA. 17 
taken of the homologies of the apical system of Echini and of the plates of 
the embryonic Comatula in its Pentacrinus stage. Neumayr's suggestion 
of the morphological value of the anal plates of the Palrechinidaa and Cida- 
ridae has thrown considerable light on this question, and shows us tlie possi- 
bility of a number of anal plates in Jlchini, say five for instance in Echino- 
cidaris, being the homologue of the dorso-central plate of the Pentacrinus 
stao-e of Comatula. Of course we should rememljer that, in making this 
homology, we are comparing plates, which while they occupy the same 
structural position, have a very diflerent physiological value. As I have 
already stated, we have the most positive proof of the origin of the dorso- 
central plate of Starfishes and Ophiurans as a single Y-shaped I'od appearing 
simultaneously with the five basals ; Init we have no such definite data either 
for the Echini or for the Couiatulaj while within the Pluteus. Such informa- 
tion would go far towards settling this disputed homology, for at present we 
are obliged to draw our conclusions from a comparison of the more advanced 
stages of development. The discovery of a pedunculated Stai^fish by the 
" Travailleur," the Caulaster of Perrier,* may throw important light on the 
homology of the centro-dorsal plate of the Starfishes and of the Crinoids. 
The discovery by Laube in the Trias of the genus Tiarechinus of Neumayr 
shows that the pyramidal anal covering, composed of a, few large plates, 
which appears in some of the earliest Crinoids known, has persisted or re- 
appeared after a long lapse of time, during which the greater part of the 
Palajchini were provided with an anal system protected by one or two con- 
centric rings of numerous plates ; this last structural feature characterizing 
nearly all the modern Echini, only a few Clypeastroids and Spatangoids, and 
among the Desmosticha the Echinocidaridge, still retaining the antique struc- 
ture of the anal system, while in nearly all Echini from the oldest to those of 
the present day we may imagine the numerous anal plates to have been the 
result of the splitting up of the five (or more?) plates of the anal pyramids 
into numerous smaller plates. Where this splitting up took place regularly, 
we have the anal system of the Pala^chinidse, Cidaridre, etc. ; where, on 
the contrary, one plate resisted, we have what exists in Salenia and all the 
recent Echini, in which one of the anal plates has a great prominence over 
the others. The Salenia-like structure, therefore, may appear at any time, 
and disappear again, Avithout perhaps having so important a morphological 
value as I was at first inclined to give it when I called attention to the 
* Comptcs Rendiis, December 26, 1882. 
