CLASSIFICATION OF ACTINIARIA 569 
Order A. Edwardsiaria. 
Order B. Zoanthinaria. 
Order C. Dodecactiniaria. 
(Sub-order (i) MADREPORARIA. 
( Sub-order (ii) ACTINTARIA. 
Tribe a. Protantheae. 
Tribe b. Ptychodacteae. 
Tribe c. Nynantheae. 
Sub-tribe a. Athenaria. 
Sub-tribe 8. Endocoelactaria. 
Sub-tribe y. Mesomyaria. 
Sub-tribe 6. Endomyaria. 
The families will be found listed under their respective 
croup on p. 542. 
4, An idea of the evolutionary history of the group has been 
worked out in connexion with the above classification, and may 
be summarized as follows. , 
It is possible to guess at a small plankton swimmer with 
eight tentacles and eight mesenteries, without much definiteness 
of musculature, and with bilateral symmetry, and contrasting 
with, not resembling, the cruciform Scyphistoma, which must 
have been quite an independent outcome of a Hydrozoan. 
This small creature would give rise to several types much hke 
itself but with differences of detail, each of which would give 
rise to a main Anthozoan sub-class. Only the one which gave 
origin to the Zoanthactiniaria need be followed here. This 
stock seemingly shed out curiosities at first ; some of them 
took to burrowing and life in cracks, and became vermiform, 
but did not amount to much (Edwardsiaria) ; others went in 
for colonialism and incrustation and had fair success in a coral- 
like way (Zoanthinaria). The main line, however, divided fairly 
early into two great groups, the split being upon the rock ot 
sluggishness and colonialism and skeleton-building versus 
comparative activity, specialization of the individual, greater 
muscularity, and no skeleton. The two groups are of course 
corals (Madreporaria) and sea-anemones (Actiniaria). There 
are a few corals which developed no skeleton, or else lost their 
skeleton, and which though often simple show colonial tendencies. 
