ECIIINOID GENUS ECHINOCOIÎYS

GENUS ECHINOCOBYS IN THE SENONIAN OF BELGIUM
7
verification, a number of other characters are often consistently attached to a
particular combination of body form, and the sum total gives the specific value.
The \ariclics arc, for the most part, based on body form alone.
Much unnecessary latitude- in body form has previously been given to certain
species, because I here had been included, unfortunately, in that species forms
which rightfully belonged to another group.
In conclusion for body form, it may be said, as one examines the comparisons
available here for size and bod} shape, that in certain groups, or along certain
lines this size and shape of the test is consistently similar and reasonably close.
It must be called necessarily a group resemblance, because it includes usually
a number of different species and varieties. On this basis one can recognize
these principal groups :
1. The conicu.s group of small and medium sized foms;
2. The marginatut-limburgicus group, which obviously includes the
earlier variety striata of vulgaris;
3. The marginatus-subglobosus-ovatus group;
4. The marginatus-gibbus-oviformis group;
5. The conuideus group;
6. The brevis to ciplyensis group;
7. The belgicus group-variable but with a persistent similarity usually
easy to recognize.
AMBULACRA.
For species the ambulacra are usually limited as a criterion, but for groups
they are quite useful. In the first place, all the ambulacra of a particular specimen
are similar. In the line of comcus-like forms, the ambulacra are furnished
with rounded pores. In earlier forms such as E. gravesi and extending into
the marginatus and brevis lines, the pores are more linear, while in conoideus
they arc' widely spaced; in belgicus conjugate and in arnaudi conjugate, widely
spaced and obliquely set. In so far as the writer is able to determine, there are
no gradual consistent changes in the ambulacra thoughout the evolution of the
Minus Application must be made for a particular species or variety after one
has proved to his satisfaction that the character is persistent for the form, and as
such is a character which can only be applied in some cases.
APEX.
The same is true of the apex as for the ambulacra. In the genus as a whole,
the apex is typically elongated. Its chief variation is an accentuation of this in
some species or groups which appears to be consistent. It is most often apparent