ECIIINOID GENUS ECHINOCOIÎYS

U
.1. S. SMISER. — A REVISION OF THE ECHINOID
The last two groups of individuals arc different, hut only in general form,
from the above. They are perfectly valid members of the species, hut have been
mistaken at limes for entirely different species, because they represent variations
which eventually lead, almost imperceptibly, into entirely different species.
Individuals of variable size but distinguished by the abruptly elevated nature
Of the summit, Selected representatives of this type grade almost imperceptibly
into marginatus as the ancestor and SubgloboSUS as the continuation. The
examples of this form are very common and have been mistaken for gibbut and
even for ovatus, to which latter they are ancestral through tubglobosus. The
base of the test in these forms is flat, but the margins are beginning to lose the
typical marginatus angularity and the anterior border in a typical individual is
Fig. i e-f. — Echinocoryi marginatus. (a) Longitudinal profile of the lype toward
/•:. iUbglObÙSU* (b) Longitudinal profile of the type toward E. gibbus. noth specimens
from the Craie de Trivière at Harmignies and both in the Musée d'Histoire Naturelle,
Brussels.
beginning to curve slightly inward toward the mouth but the base is not typically
retracted as in E. gibbus.
The last group of individuals is very similar to E. gibbus and appear to he
ancestral to thai species. They show the beginning of the retracted base characteristic
of gibbus hut have not, as yet, acquired it's gibbosity and still maintain
lh.> more abrupt flanks of marginatus.
In spite of the variable groups Echinocorys marginatus is distinct as a species
and after one has become familiar with the group as a whole they all have an
almost (indefinable marginatus look which is a combination, or I he sum total of
the following characters : oval marginal pcriproct, angular borders, oval
(somewhat pointed posleriorly) contour, elevated upper surface proportional to
width and length (expressed in percentage on the basis of 100, I he relation of
height, width and length will be a proportionate comparison as represented by
these figures, length 50 percent; width 45 percent; height 40 percent).