FEATHER-STARS, RECENT AND FOSSIL. 
203 
especially marked in the Cretaceous species ; for while some 
Oolitic forms have really large external basals, this is not the 
case in any Cretaceous species, while they are occasionally 
absent altogether. As, however, we are unable in these cases 
to see the interior of the calyx, it is impossible to determine 
whether a rosette is present or not. It is the same with 
the only two Tertiary species the calices of which are known 
to us. 
We cannot, therefore, say with certainty when the Comatuloe 
first ceased altogether to retain their larval basals on the exterior 
of the calyx, as Pentacrinus species do still (though some of them 
formerly did not), and as most of the Oolitic Comatuloe did. 
It is certain, however, that the final change occurred after 
the middle of the Cretaceous period ; for Antedon Lunclgreni, from 
the Upper Chalk, had Pentacrinus- like basals appearing exter- 
nally. The disappearance of the basals from the exterior of 
the calyx was not completed, therefore, even at this compara- 
tively recent date ; and it is just possible that a very remark- 
able species, now living (?) in the Indian Ocean, may be the 
last survivor of this more generalized form of Comatula, with 
Pentacrinus-like basals and no rosette. Unfortunately but one 
example of this species has ever been discovered. Fifty years 
ago it was dissected, and a description was written of it ; 
hut it is not complete enough to enable us to settle this 
interesting question. At any rate, none of the deep-sea 
Comatuloe brought home by the Challenger have any resemblance 
to the older species, every one of them having a rosette. 
Other questions which naturally arise are the following : 
For what reason did the basals of Comatuloe cease to be five 
more or less separate pieces and undergo transformation into 
the rosette ; and why is it that Pentacrinus and Comatula have 
varied in different directions ? All recent Pentacrinus species 
have external basals, but some fossils have not. Some fossil 
Comatulce have them and others have not ; but they do not 
appear in any recent forms (with one possible exception), for 
the larval basals never become prisms or wedges the outer ends 
of which remain external like those of Pentacrinus, hut they 
disappear altogether into the interior of the calyx. These ques- 
tions must remain unanswered, at any rate, for the present, if 
not permanently. 
It may be pointed out, in conclusion, that in the class 
Crinoidea, as in so many other groups of animals, the recent 
forms are the most highly specialized ; and the further we go 
hack in geological time, the more nearly (on the whole) do the 
Comatulce approach Pentacrinus and other stalked Crinoids to 
which they have so much resemblance in their early stages of 
development. 
