529 T. A. STEPHENSON 
retractor or pad as in all other Ilyanthids. The body-margin 
is notched in a way suggestive of acrorhagi. In fact, but for 
its burrowing habit and rounded end, it would be a typical 
member of the Actiniidae of the less muscular sort. Whether 
it is an Ilyanthid which has passed the usual grade of develop- 
ment and moved towards that of adherent forms, or whether it is 
a retrograde adherent which has gone back to buried life and 
lost its base, we cannot tell. But in classification it ought to 
be separate, or probably go nearer the early Actiniids than the 
Ilyanthids. I have in this paper made a family Andresiidae 
for it, placing this among the earlier Endomyaria (see Part IT). 
With regard to other forms without bases excluded from the 
Athenaria (see Part I) these fit in better with the Mesomyaria - 
(see pp. 541, &c.) than with the Athenaria, because of their 
acontia and mesogloeal sphincter, &c. In the case of some of 
them (Phelliidae in part) we have our finger on the transition 
from burrowing to adherence, and there are grades from 
a physa to a well-marked base ; and as these seem to be getting 
up to the attached stage it seems better to keep them out of 
the Athenaria, especially since their acontia and mesogloeal 
sphincter and other things show their relationship to be with 
the Mesomyaria. Some of the Diadumenids are also almost 
without base, but here it is obviously a case of retrogression or 
arrested development; they are probably normally adherent 
forms changing under special conditions. 
§G. The Endocoelactids. 
These forms start from a six-pairs-of-muscular-mesenteries 
or Halcampa-stage basis, with ciliated tracts on the mesen- 
terial filaments, but work onward from this in quite an unusual 
way. The secondary mesenteries appear in the endocoels 
of the lateral primaries, and all of them have the character of 
directives (i.e. the retractors of each pair face away from one 
another). The usual plan is, of course, for the secondaries to 
appear in the primary exocoels, and have their retractors 
vis-&-vis. The contrast is indicated in Text-fig. 16, @ being 
an Endocoelactid. Apart from this most fundamental structural 
