ECIIINOID GENUS ECHINOCOIÎYS

48 J. S. SMISER. — A REVISION OF THE ECHINOID
stratigraphic observations on the genus. And in the study of Echinocorys, their
relations and evolution, certain facts regarding their stratigraphic distribution
have been determined. These 'hidings are reported here with an unprejudiced
attempt to give them their true value and no more.
As regards the evolutionary development, and the relationships of the
various members of the genus, one is on much more solid ground, although the
final result may be theoretical. In support of this fact, the reader's attention is
called to the enormous amount of material, thousands of specimens, of this genus
which exist in the various Relgian collections. With this magnificent amount
of material representing the genus and its ramifications, it is entirely reasonable
to assume that most of the picture of its development exists in this material.
And in so far as a treatment of development and relations is concerned, one can
follow it on the basis of a general knowledge of stratigraphic distribution.
EVOLUTION.
The Echinocorys of the Relgian and adjacent Senonian have, as their most
logical ancestor Echinocorys gravesi. This species is not represented in Belgium
but seems to have first been common in the seas depositing the rocks now know n
in adjacent areas as the beds of Micraster leskei and Holaster planus. It is
abundant in the beds of this same level in northern France and associated with
an abundant occurrence of Micraster leskei but Holaster planus is rarer in theupper
Turonian beds of northern France. In explanation it would be well to
explain that in the upper Turonian, the Micraster leskei beds have been at limes
miscalled Micraster breviporus beds (see explanation of Plate 1).
These upper Turonian beds, where are associated the Micraster leskei, E. gravesi
and some H. planus are the very uppermost Turonian and form an unmistakable
starting point for the earlier development of Echinocorys. This confusion
of the upper Turonian occurrence of Micraster leskei is unfortunate. It has
resulted from the confounding of these two similar Micrasters in the earlier
Iit.Mature. As stated in another place (see explanation of Plate 1) these two fornIs
are commonly treated by stratigraphers as synonymous. And in reality the
form which really represents the so-called « Micraster breviporus » is not a
different species at all, but is the young of Micraster coranguinum. This latter
species occurs commonly at a much higher level and between its occurrence and
the Micraster leskei beds the beds of Micraster decipiens intervene. Echinocorys
gravesi continues, in a much more limited manner, into the Coniacian of northern
France, where it is associated with Micraster decipiens and its own
descendants E. vulgaris and varieties. It is very limited in these beds as inferred
from its representatives in the collections as compared with the whole echinoid
fauna. During the Coniacian, in the beds characterized by Micraster decipiens,
there developed from E. gravesi by extension of the base, and elongation of the