76 



tliev are allached lo Ihe conipe'n.salioii-.sac, which has arisen either as an in- 

 vagination or as an oulpusliing from thai cover. In SteyannporclUt, ThdUtmoporelUi 

 and Micropnrti iincifera they are represented by a single iiundie on eadi side 

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

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

 able is their appearance in Microporiiui horcdlis, as they here unite the crypto- 

 cyst with its covering membrane but are otherwise, as in Malacoste(j(i, placed in 

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

 closer investigation might prove a tlistinguishing character, namely the »suboral 

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

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

 in some few sj)ecies, as in Cheiloponi sinceni and SiuiUiiid paliuatd, 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 liand is an organ of very great systematic importance, as it 

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

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

 poreUd, Iiwersiiila, Haplapoiud, Adeniui, Adeonellnpsis, Cdlwellid, Onchoponi, Oiuho- 

 porelld, Tuhiicelldria) not immediately ])r()ximally to the operculum, hut through 

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

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

 Micro[)()reII)i. 



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

 skeleton can not be expressed cjuite 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 liircl- 

 Iciriidiic and Fliistriiilde in which the frontal wall is wholly or mostly uncalciticd, 

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

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

 in the BiceUarildde. The families Adeonidde and Miiriozoidde are diaracterized bv 

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

 is undoubtedly to be found in the lieteporidae and Sclerodomidae. The dilference 

 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/ 1 



