73 



iiula and llie iiicrusting Micr. cilidtct us well as between a (Veely growing, richly 

 branched Japanese Micropnrella wliich is closely related to M. Mdlusi, and the 

 last-mentioned, as a rule incrusting species. Genera based on the presence of 

 radical fibres (e. g. Craspedozoiiin, Fliislrainorplui) will for these reasons be just 

 as artificial as genera based on the lorni of the colony, but this does not ex- 

 clude that differences in the appearance of the radical fibres may sometimes be 

 of use as auxiliary characters, e. g. in some genera of the family Bicellariidae. 

 A much greater systematic importance must be given to the flat kenozooecia, 

 which in all freely growing Releporidac not only form the incrusting part of the 

 colony but also a covering of its basal (as a rule the outer) suiface. Although 

 on account of their position they can only occur in freely growing species, they 

 are namely characteristic for the family Heteporidae, and are found in all members 

 of this family, occurring as free colonies. A still greater systematic importance is 

 held by the lateral chambers, so characteristic of the family Catenariidae, which 

 may appear in each zooecium up to four in number on each side, and which 

 besides the imj)ortance they have for the distinction of the family also in many 

 cases offer good generic and specific characters. 



The Heterozooecia, as is known, may sometimes occur independent or vicarious, 

 taking the place of a zocrcium in the colony, sometimes dependent and situated 

 on the zoa'cia, and in the last case they may in one way be regarded as organs 

 belonging to these. The vibracles, which appear on the basal wall in Caberea and 

 other genera of the family ScnipoceUariidne, occupy a peculiar intermediate posi- 

 tion between the independent and dependent heterozooecia ; for while in other 

 cases the latter are always connected with the zocecia by a common wall, these 

 vibracles have an independent basal wall, and can therefore be separated from 

 the zocecia. The ditTerence between independent and dependent heterozoa^cia is 

 of systematic interest, in that certain systematic divisions (families and genera) 

 only have independent heterozoa'cia, others only dependent, while again others 

 present both kinds, not seldom in such a way that they occur together. The 

 independent Iieterozoojcia have their main extension in the division Amiska, 

 where thev' appear unmixed in the families: Flustridae, Cellidariidae and Tlmlamo- 

 porellidtw, l)esides in the genera Ouijchocella, Scleuaria, Cjipiddrin and Liuuildria: 

 The majority of the Membraniporinn and (jibrilinci forms may have dependent 

 heterozocEcia, though independent ones do appear in not a small number of 

 species, e. g. in Membraniporinn crassimarijinattt, M. cnrniyera, M. pijruhi, M. plana, 

 M. velaUt and in Figulinu (igidaris. While all the other species of the genus 

 Callopora have dependent heterozooecia, we find at the same time independent in 

 C. craticula. Independent heterozooecia seem to occur in all members of the 



