161 



in A. monoceros. It is in lliis s[)ecies seen al the bottom of tlie nperlure nearly 

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

 ciiim. 



As I cannot discover any relationship between Hianlopora 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 Aracli- 

 iiopnsia, but on a new basis, and I think it may for the present l)e ranked under 

 the above mentioned artificial family ('.lihriliiiidae. 



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 usualh' 

 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 wdiich a parietal muscle passes out to the covering membrane. 

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

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

 join the basal (sometimes a lateral or the distal) wall in dilTerenl exlcntion. 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 tubes enclosing a part of the polypide. 

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

 chitinized opercular valve. The avicuhiria or vibrncula are always independent. 

 There may be hyperstomial, endozocrcial endofoichal or bivalvular oarin. 



The families Microporidae, SteijanoporcUidae, Aspidostomidae, Tlialaiiioporellidae, 

 Selosellidae, Chlidoniidae and Alijsidiidae 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 

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

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

 |>rcsent or wanting and spines may appear. There may be (ivicnhiria, and the 

 o(vcia, when present, are endozoa^cial 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 



n 



