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in which the heterozocecia are either constantly occurring or always absent and 

 in that case their appearance or absence will help to characterize the repective 

 families or genera. For instance the absence of avicularia is to such a degree 

 bound up with the notion Electra, that the discovery of an avicularia-bearing Eledra 

 species would rightly be looked upon as very remarkable. We may mention the 

 Adeonidae, Catenariidae, Celleporidae, Holoporellidae and Thalamoporellidae as ex- 

 amples of families with constantly occurring avicularia, while these are absent 

 in the Aeteidae and Steganoporellidae. They appear for instance constantly in the 

 genera Callopora and Exochella, while they are absent in the genera Membrani- 

 pora (s. str.) and Electra. 



The ocecia present a similar inconstancy in their occurrence to the hetero- 

 zocecia, as they are quite absent in a number of families (e. g. Adeonidae, Stegano- 

 porellidae and Aeteidae), genera (e. g. Beania, Membranipora (s. st.) Cupularia and 

 Lunalarid) and species, and in many species they appear very inconstantly and 

 by no means in all the colonies. For instance, in Discopora verrucosa we only 

 find ooecia in the colonies from deeper water, never in coastal forms. There- 

 fore a genus or species cannot be based only on the difference, that they have 

 or are without ooecia, whereas a constant occurrence of these formations can be 

 used as an auxiliary character. What has been said about the systematic value 

 of the fact, that heterozocecia or ooecia occur in a species, genus or family, does 

 not exclude the different structure of the heterozocecia and the ocecia from having 

 a great systematic importance and we shall discuss this matter further in the 

 following sections. 



With regard to the kenozooecia, their systematic importance is very diverse, 

 and the small triangular spaces for instance, which appear between the zooecia 

 " in different forms, are not always constant in the species. This applies for ex- 

 ample to Membranipora Lacroixi. That the so-called radical fibres, which serve to 

 fasten freely growing colonies of less solid materials, only have a very slight system- 

 atic importance, is evident, partly from the fact that they are found in so many 

 families (e. g. Flustridae, Bicellariidae, Cellulariidae, Scrupocellariidae, Catenariidae 

 etc.), partly because their occurrence is dependent on the free condition of the 

 colony, which has no systematic importance. We may give here a few examples 

 to show that the radical fibres can be present or absent in forms of growth of 

 the same species as well as within closely related species. Such radical fibres 

 can for example be found in Steganoporella neozelanica, which occurs in pillar- 

 shaped trunks, while they are absent in an incrusting form, which Harmer 

 considers as a variety, var. magnifica, of the same species. A similar relation is 

 found between the freely growing species: Microporella flabellaris and Mic. margi- 



