76 



they are attached to the compensation-sac, which has arisen either as an in- 

 vagination or as an outpushing from that cover. In Steganoporella, Thalamoporella 

 and Micropora uncifera they are represented by a single bundle on each side 

 reaching to the covering membrane through the two openings (»opesiulae« Jull.) 

 in the cryptocyst, which appear in the forms mentioned, and still more remark- 

 able is their appearance in Microporina borealis, as they here unite the crypto- 

 cyst with its covering membrane but are otherwise, as in Malacostega, placed in 

 two longitudinal rows. Waters^ has pointed out another structure which on 

 closer investigation might prove a distinguishing character, namely the »suboraI 

 glands*, which are placed on each side proximally to the operculum. They seem 

 to appear in most Ascophora, although according to Waters they may be absent 

 in some few species, as in Cheilopora sincera and Smittina palmata, whilst up to 

 the present they have not been found within the Anaska. While all the organs 

 mentioned only presumably present distinguishing characters, the compensation- 

 sac on the other hand is an organ of very great systematic importance, as it 

 is the means of separating the CheUostomata into two main divisions: Ascophora 

 and Anaska. Against the common rule, it opens in a number of genera (Micro- 

 porella, Inversiula, Haplopoma, Adeona, Adeonellopsis, Calwellia, Onchopora, Oncho- 

 porella, Tubiicellaria) not immediately proximally to the operculum, but through 

 a median pore (Ihe Ascopore) further back, and a number of these forms (the 

 species of Haplopoma, Adeona and Adeonellopsis) have been wrongly referred to 

 Microporella. 



Calcification. Though the difference in firmness or density of the calcareous 

 skeleton can not be expressed quite exactly except by the aid of chemical ana- 

 lysis, it is in many cases already so distinct from a general zoological examina- 

 tion, that it must be regarded as a good auxiliary character in the distinction 

 of a number of families. We find the weakest calcification in the families Bicel- 

 lariidae and Fliistriidae in which the frontal wall is wholly or mostly uncalcified, 

 but on the other hand in the family Onchoporidae, the members of which have 

 a completely calcified frontal wall, the calcification is not much more solid than 

 in the Bicellariidae. The families Adeonidae and Myriozoidae are characterized by 

 very thick- walled zocecia, while the very firmest and hardest calcareous substance 

 is undoubtedly to be found in the Reteporidae and Sclerodomidae. The difference 

 in regard to the firmness of the calcareous skeleton seems to be very slight 

 within all natural families and must therefore be regarded as a good expression 



' 108 a. 



