No. 4.] MORPHOLOGY OF THE ACTINOZUA. l6l 



eighty-eight in Protauthca, 1 being imperfect, and the ciliated 

 lobes are lacking in their mesenterial filaments. On account 

 of these peculiarities it seems to me that these two forms 

 must be grouped together in a family, Gonactiniidae, as Carl- 

 gren ('93) has proposed, and Halcurias cannot be placed with 

 them. The family Gonactiniidae must, I believe, be placed 

 among the Hexactiniae, as indeed must all the forms which I 

 have included in the past in the order Protactiniae, as well as 

 those which Carlgren has referred to the Protantheae. The 

 discovery of hexactinian mesenteries in certain Edwardsiae, 

 already referred to, necessitates either the abolition of both this 

 order and that of the Protactiniae, or else an extension of the 

 latter to include both the Edwardsiae and many of the Hal- 

 campidae, and it seems to me that the former step is the most 

 practical and the most in accord with a correct phylogenetic 

 scheme. Not that I mean by this that the stages of develop- 

 ment shown by the members of the group do not represent 

 phylogenetic stages in the evolution of the Hexactiniae. Cer- 

 tainly no one will imagine that what has so long been regarded 

 as the Edwardsian type of structure is not in reality a primary 

 phylogenetic condition, even though we are now obliged to 

 regard the existing Edwardsiae as true hexactinians which 

 secondarily in some cases may represent the more primitive 

 condition. 2 The facts of embryology speak too strongly re- 

 garding the Edwardsian stage to allow of question as to its 

 past occurrence, and I believe that there can be as little ques- 

 tion regarding the stages which I have supposed to intervene 

 between the Edwardsiae and the typical Hexactiniae, even 

 though the forms which to-day represent these stages do so 

 possibly only on account of secondary modifications. 



1 Protanthea has four imperfect mesenteries which make pairs with the four 

 lateral perfect mesenteries, and twelve others arranged in pairs in the primary 

 exocoels, all being fertile and provided with mesenterial filaments. In addition to 

 these there are, however, as in Halairias, a number of short, narrow mesenteries 

 confined to the upper part of the column and standing in relation to the tentacles, 

 of which there are about ninety-six. 



- Compare Van Beneden, Les Anthozoaires in Ergebnisse der in dem Atlan- 

 tischen Ocean, etc., ausgefuhrten Plankton-Expedition der Humboldt-Stiftung. 

 II. 1898. 



