THE TRENTON CRINOID, OTTAWACRINUB 
9 
to them in position in the four other rays. But in each ray those 
plates now seem to me to be the upper and lower half of a com- 
pound radial (Rs and Ri). This view is based on facts which 
were not fully apparent before the specimen itself was cleaned 
and examined. First, the upper plates are quite as wide as the 
lower at the line of junction. Secondly, the union of the two 
plates along the suture just mentioned seems to be closer than 
the union along the suture immediately succeeding. In these 
respects the right-hand of Mr. Billings’ two drawings of the 
crown and my own previous analysis convey a false impression. 
Thirdly, the upward tapering of the plates here regarded as IBrj, 
is in most rays more rapid than that affecting the plates regarded 
as Rs and Rz. 
If, then, the present interpretation be correct, the two proxi- 
mal elements of r. post, ray are, as in so many allied genera, the 
Radial proper (derived from Rs) and the Radianal (derived from 
Ri). The peculiarity of the interpretation lies in the view that 
all the other radials are horizontally bisected. 
The interpretation of the radials here adopted has an important 
bearing on crinoid morphology. In 1900 (“Treatise on Zoology,” 
III, Echinoderma, p. 112) I quoted Ottawacrinus a3 a Dicyclic 
genus in which some of the radials had been shifted so as to lie 
almost vertically above the basals; and I continued: “The 
suggestion then is that the inferradials and basals of Monocyclica 
represent basals and infrabasals respectively of Dicyclica, If 
then the Rs and the R i fuse, a truly monocyclic type is produced 
with one circlet of BB and one of RR. One obvious objection to 
this theory is the presence in many Dicyclica of a plate (the 
radianal, RA), which is now generally regarded as a slightly 
modified inferradial.” In putting forward that hypothesis as a 
possibility, I had in mind evidence other than Ottawacrinus , long 
since submitted to me by a foreign colleague, but not yet pub- 
lished by him. Now, so far as Ottawacrinus is concerned, it not 
merely ceases to be evidence for the hypothesis, but becomes the 
strongest evidence against it. If it be the case that inferradials 
coexist in this genus with basals and infrabasals, it is obvious 
that they cannot be homologous with basals. 
It has been suggested to me that Ottawacrinus may have some 
connexion with the Flexibilia Impinnata. The somewhat close 
lateral abutment of the proximal brachials as well as of the 
