71 



answered absolutely in the negative, as agreement in regard to the form of colony, 

 according to the data given above does not give any guarantee for real rela- 

 tionship. 



When Norman points out the inconsistency of rejecting the form of colony 

 as a systematie character in the Cheilostomata though it is used in the Cijclo- 

 stomata and Ctenostomata, we must remark that as the zooecia within the division 

 of the Cyclostomata have nearly the same structure, it has been necessary to 

 choose the characters from the way in which these zooecia are arranged. I do 

 not doubt however that the classification of the Cyclostomata also requires reform. 

 I shall not in this work enter further into this question however, but only men- 

 tion as an example that a new species from the Danish cretaceous formation 

 Diastopora carinata, may appear both as round discs and as free cylindrical stems, 

 which sometimes have a wide inner cavitj', sometimes an axial canal, fine as 

 hair. This species may thus be referred both to Diastopora and to Cauaria. An- 

 other species, Diastopora compressa, occurs both as unilamellate and as bilamel- 

 lata expansions, and would consequently be referred to Diastopora as well as to 

 Mesenteripora, the latter of which genera P erg ens even refers to another family. 

 On the whole, the classification seems to me more natural within the Ctenosto- 

 mata. For the rest, in dealing with the classification it is impossible to be consi- 

 stent in the sense that we must everywhere attach the same value to the same 

 structural feature. It proves on the contrary that the same structural feature in 

 different systematic divisions can have a very different systematic importance, 

 so that characters which are constant in one genus or family in other corre- 

 sponding divisions are not always constant even within the species. 



The occurrence of one or several forms of individuals in the colony. 



The fact, that a colony can contain one or more forms of individuals, which 

 are absent in another, does not exclude the possibility, that the two colonies can 

 belong to the same genus, or even to the same species. Considering first of all 

 the heterozooecia, their occurrence in many cases is, as known, very inconstant 

 within the family, genus or species, because they can be absent in more or fewer 

 genera within the family, and in more or fewer species within the genus. Even 

 within the species their appearance is often inconstant, and we may cite the 

 following species as examples, in which they can sometimes be absent, some- 

 times present: Schizoporella unicornis, Sch. sangvinea, Escharina simplex, E. Alderi, 

 ^Lepraliao- Pallasiana, L. pertusa, L. edax and Discopora verrucosa. We can there- 

 fore not base a genus, nor even a species on the presence or absence alone of 

 heterozooecia. On the other hand, there is a whole series of families and genera. 



