30 
Bather). Though this has already been done by several authors 
(Lovén, Agassiz, the Sarasins, Neumayr), I think the 
revision of the question given here will prove not to be superfluous, 
partly in view of the several new facts brought forward of later 
years, partly because my interpretation of some of the facts and 
statements differs not inconsiderably from that of my predecessors. 
The Palæechinoidea (— the name used in its wide 
sense —) have no central plate, so far as known. In those forms 
of which the apical system is known, there are circles of small 
plates, arranged along the border of the anal area, and it seems 
scarcely too hardy to suppose that they all had their anal system 
built after this plan, without a central (suranal) plate. In the 
Cystocidaroida the whole apical system appears even to be totally 
wanting, a fact which, as is rightly pointed out by Gregory, 
»appears fatal to the theory assigning a crinoid ancestry to the 
Echinoidea" 1). and to the homology between the plates of the 
apical system in Echinoids and those of the calyx in Crinoids. 
A. Agassiz (Calamocrinus Diomedeæ. p. 72?) suggests that 
»while it is true....that the apical system of the Palæchinidæ, 
as far as the adult is concerned, presents no trace of the anal 
plate so prominent in young Echinoids, and which is permanent 
in Salenia, yet there is nothing to show that the young of those 
genera did not possess, like the Euechinoidea, a single central 
anal plate in their earliest stages". The facts known from the 
other Echinoids, as set forth below, seem to me, on the contrary, 
to show that there is no probability at all for supposing that the 
young stages of the Palæechinoids did possess a single anal plate. 
Agassiz also expresses this latter meaning later on in the same 
paper (p. 83): ,,the history of the plates of young Cidaris .... is 
decidedly opposed to this view". Thinking to have proved that 
the young Cidaris has five radial anal plates (infrabasalia), he con- 
1) I W. Gregory. On Echinocystis and Palæodiscus — two Silurian 
Genera of Echinoidea. Quart. Journ. Geol. Soc. LIII. 1897. p. 132. 
?) Mem. Mus. Comp. Zool. XVII. 1892. 
