ZOANTHARIA 



must notice, that a specimen expanded broadwise gives quite a different appearance from a specimen 

 with mesenteries contracted broadwise. The parieto-basilar muscles seem generally to be weak, 

 sometimes they may be more differentiated, but are on the whole of small importance for classification. 

 The distribution of the longitudinal and the parieto-basilar muscles on the body-wall is sometimes 

 small, sometimes greater and is sometimes of use for the separation of the species. The macro- 

 mesenteries project more or less into the gastrovascular cavity, so that it would seem as if this might 

 be a fairly useful character. It must be pointed out, however, that the appearance of the mesenteries 

 is quite different in contracted and expanded specimens of the same species and it is also of import- 

 ance in the same respect whether the sexual organs are developed or not. If the sexual organs are 

 much developed, namely, the mesenteries are considerably broader than is otherwise the case. 



The structure of the filaments is of no great use for the classification of the species, as it is 

 mainly the same in all forms. 



As has been pointed out, there is great uniformity in structure and appearance in most of the 

 species within the genera, for which reason the identification of many species is distinctly difficult- 

 As most of the Zoanthidae are besides incrusted so much, that in many cases it is quite impossible 

 to get moderately good sections, it is obvious that the identification of Zoauthidae-species and the 

 setting up of new species is in most cases a matter of considerable difficulty. It was of great import- 

 ance, therefore, to find some more pecularities of organisation, which showed such great differences 

 in the different species, that they could be used for their identification. As I have found regarding 

 the Actiniaria, that the structure, size and arrangement of the nematocysts provide good characters 

 for identification, I have investigated if the same was the case in the Zoantharia. Even if this is not 

 so much the case in the Zoantharia as in the Actiniaria — as the first-named show great uniformity 

 probably even in the nematocysts, the structure, size and arrangement of the nematocysts in the 

 Zoantharia may nevertheless contribute to the identification of the species. As in the Actiuaria there 

 may certainly be some species of a genus which have almost the same distribution, structure and 

 size of the nematocysts, whereas other species may show great differences in this respect. As the 

 length and breadth of the nematocysts seem to be constant — of course with a certain amount of 

 variation - - the measurements of the nematocysts are in my opinion more suited to the determination 

 of a species than most of the measurements of Zoanthidae, even more suited than most of the other 

 structural characters, though of course with certain exceptions. In the following I have also taken 

 account of the nematocysts as far as possible in the description of the species. Especially the large 

 nematocysts with much coiled spiral threads, which are found in the body wall and filaments, some- 

 times in the tentacles and the oesophagus, appear to be of varying size in the different species. It 

 must be observed that the range of variation seems great in certain cases. It is possible, however, 

 that this condition is only apparent. I cannot set aside the possibility, namely, that some of the 

 large nematocysts with greatly twisted threads, which have a thinner wall than the other capsules, 

 may to some extent change their dimensions in different liquids of preservation, i. e. not be quite 

 resistant. The relation between length and breadth would thus be different in varying degrees of 

 contraction. I cannot however express my opinion on this point with certainty, as none of the exper- 

 imental proofs in this respect could be made by me. Without denying the possibility that the large 



