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in A. monoceros. It is in this species seen at tlie bottom of tlie aperture nearly 

 on a level with the spines and separating the ooecium from the proximal zoce- 



cium. 



As I cannot discover any relationship between Hiantopora ferox and Cribrilina 

 monoceros, but find the peculiarities of the latter species sufficiently well-marked 

 to make it represent a genus of its own, I shall keep Jullien's genus Arach- 

 nopusia, but on a new basis, and I think it may for the present be ranked under 

 the above mentioned artificial family Cribvilinidae. 



2nd Division: Coilostega. 



The frontal wall has within the covering-membrane a generally depressed, 

 calcareous cover (the cryptocyst) surrounded by projecting margins, which either 

 reaches the proximal margin of the operculum or is only separated from the 

 latter by a small membranous portion. Spines of the usual form are usually 

 wanting. The cryptocyst is as a rule provided with pores and most frequently 

 with a foramen, the »opesiula« (sometimes confluent with the aperture) on each 

 side, through which a parietal muscle passes out to the covering membrane. 

 These foramina may be either simple perforations of the cryptocyst, or out- 

 growths from their proximal and inner margin may sink into the zooecium to 

 join the basal (sometimes a lateral or the distal) wall in different extention. In 

 most cases these »opesiular outgrowths*, as we may call them, form in connec- 

 tion with the interjacent frontal wall and generally also with the basal wall a 

 more or less complete tube, the »polypide tube«, enclosing a part of the polypide. 

 There is either a wholly chitinized, simple operculum or a partially strongly 

 chitinized opercular valve. The avicularia or vibracula are always independent. 

 There may be hyperstomial, endozooecial endotoichal or bivalvular ocecia. 



The families Microporidae, Steganoporellidae, Aspidostomidae, Thalamoporellidae, 

 Setosellidae, Chlidoniidae and Alysidiidae belong to this division. 



Family Microporidae. 



The semi-circular aperture, which is bounded proximally by the distal, 

 ascending margin of the cryptocyst, has generally a more or less strongly 

 chitinized (or calcareous), simple operculum, more seldom an opercular valve. 

 Opesiulse, when present, are always distinct from the aperture. Pores may be 

 present or wanting and spines may appear. There may be avicularia, and the 

 ocecia, when present, are endozooecial or hyperstomial. 



The family Microporidae is, in contrast to the following families, not quite 

 natural, comprising as it does a series of genera which have independently 



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