CKRIANTHARIA. 



39 



In the first sub-order he includes not only the forms that posses "acontia" but also those which in 

 the adult state are known not to posses any, e. g. Cerianthus mcmbranaceus and several species of 

 Pachycerianthus. As far as I can see, Me. Murrich has here fallen into error, for there is nothing 

 in the development of the Ceriantharia to point to the "acontia" being larval organs, that afterwards 

 disappear in the full-grown individuals. On the contrary it is possible that the "acontia" in some cases 

 shew themselves quite late in the course of development, and most probably their number increases 

 with the growth of the animal. In reality Me. Murrich's diagnosis of Acontiferae conflicts seriously 

 with van Be tie den's. 



Whilst Me. Murrich says of Acontiferae that "they are provided with acontia at least during 

 the early stages of development", we find in van Beneden's diagnosis of the three genera Solaster- 

 actis, Apiactis and Peponactis, that the acontia are "absentes ou tardives", a view quite contrary to 

 Me. Murrich's. As we know besides that the majority of Ceriantharia, so far anatomically des- 

 cribed, lack acontia and botrucnidae alike, we have at once a strong reason for removing these Ceri- 

 autharia from the group Acontiferae. It seems to me necessary therefore to expel the whole of Me. 

 Murrich's Cerianthidae family, and a great part of the Arachnactidae family as well, from Acon- 

 tiferae, thus reducing it so considerably, that it would only be found to include some adult forms. 

 In my opinion then Cerianthidae should be divided into three groups. 



(1) those that possess neither botrucnidae nor "acontia". 



(2) those that possess "acontia" but not botrucnidae. 



(3) those that possess botrucnidae but not "acontia". 



To the first group belong Me. Murrich's Cerianthidae and a part of his Arachnactidae. 



Me. Murrich divided Acontiferae into 2 families Cerianthidae and Arachnactidae. In the 

 former the second couple, reckoning from the directive chamber, would be the longest mesentery 

 couple (the telocnemes) of the protomesenteries, in the latter family on the other hand the fourth 

 couple would be "the telocnemes". This characterisation does not seem to me quite satisfactory even 

 if we apply it only to the two adult genera included by Me. Murrich, Cerianthus and Pachyccri- 

 anthns, and this among other reasons because the fourth couple in my opinion belongs not to the 

 protocnemes but to the metacnemes (deuterocnemes, metamesenteries). Between Cerianthus and Pachy- 

 ccrianthus, which are doubtless real genera, there is a distinct difference however, as Me. Murrich 

 has clearly recognized, namely, that whilst in the genus Cerianthus the second couple of protocnemes 

 is long, fertile and similar to the metacnemes of the ist cycle (M), in the genus Pachycerianthus ou 

 the other hand, the same couple is short, sterile, and provided with a well developed cnido-glandular 

 tract like the metacnemes of the 3rd and 4th cycles (B, b}. 



Me. Murrich's diagnoses, too, of the genera Cerianthus and Pachycerianthus are not so distinct 

 as might be wished. As to the genus formulated by Roule and accepted by Me. Murrich, Pachy- 

 cerianthus, it is extremely difficult to form from Ro tile's description an adequate idea of the mesen- 

 terial appendages (the filaments and the "acontia"), with which it is far more important to be ac- 

 quainted than with some of the generic characters mentioned by Roule. Roule (1904) characterises 

 the genus in this way "cloisons courtes, deux seules d'entre elles (S 3 = fourth couple) parviennent 

 dans 1'extremite aborale. Cloisons directrices epaisses donuent a la lage directrice la forme cl'un canal 



