560 T. A. STEPHENSON 
From this point evolution among the Halcampa-descen- 
dants or Nynantheae may be further considered. 
About the Athenaria and Endocoelactaria little further need 
be said beyond what may be found in the special sections on 
those forms. The Athenaria are highly muscular as regards 
their mesenteries, this being useful in a burrowing existence. 
They have diverged among themselves in curious ways, and 
some of them present rather interesting special features, such 
as the immense siphonoglyphe and conchula of Peachia 
(presumably a development connected with drawing in a water- 
current when the animal is below the sand), and the knobbed 
tentacles of Eloactis. Harenactis has become very 
attenuated, with many cinclides—and indeed there are often 
cinclides among these forms. The Endocoelactaria are obviously 
divergent in another way. ‘The earlier ones, most nearly 
represented by Carlgrenia, would be not far from the 
Halcampa-stage, but with secondary mesenteries (micro- 
cnemes at first) appearing in the lateral endocoels, and oriented 
like directives—this modifying the whole plan of structure. 
A stage further is represented by Haleurias, with ten pairs 
of macrocnemes instead of six, and later in the Actinernids the 
distinction into macro; and microcnemes has gone and numerous 
mesenteries are perfect, and often there are lobed dises, swollen 
tentacles, thick body-walls, and deep sea habitat. A sphincter 
never appears. 
This leaves the main mass of forms, the Meso- and Endo- 
myaria (including Stichodactylines). With regard to the 
justifiability of these two groups, if the work of this paper and 
of Part I be taken into consideration it should emerge that 
so far as we can know anything about these things, the Endo- 
myaria did, as a bunch, follow a different line of tendency 
from the Mesomyaria, and if that is established the grouping 
follows. It is mainly a difference of tendency, there being, at 
any rate low down in the two groups, probably no essential 
histological difference—this might come in higher up, perhaps, 
in comparing such formsas Actinoscyphia and Catadio- 
mene with Thalassianthus. 
