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porliuil than the helerozoa'cia. While these very seldom present family or generic 

 c-haraclers and it is for instance unusual to meet such peculiar, or in their 

 character so constant, avicularia as those we find in the families Bicellariidae 

 and Adeonidae, the oa'cia in most families and in a number of genera present 

 systematic characters of greater or less importance. We might here recall the 

 oci'cial structure in the families Fliislridae, Farciminariidae, Bicellariidae, Cellnla- 

 riidae, Thidamopovellidae, Catenariidae, Hippothoidae, TubiicelUiriidae, Onchoporellidae, 

 Alysidiidae, etc. The most widely distributed oa'cial type is the hyperstomial, 

 which again may present a series of different modifications. While thus the 

 od'cia in the Bicellariidae and Releporidae are free, they are as a rule connected 

 with the zofccium in the larger part of their basal wall. Other dilTerences are; 

 that the ectoooecium may be membranous or calcareous, and that the calcareous 

 surface of the occcium may be entire or provided with pores, though the last- 

 mentioned characters are not of the same use everywhere and present many 

 exceptions. While the ectooa-cium in the genus Scrupocelhiria may sometimes be 

 entire and sometimes with pores, it is generally provided with pores in the 

 genera CeUepora, Discopora, Hippothoa and Siuittina, and only a very few species 

 are exceptions from this rule. In the large family Releporidae the ooecia are 

 either entire or provided with a linear or three-foliate Fissure, and only one 

 single species is further provided with a few scattered pores. 



Anatomical characters. These are the characters derived from the organs 

 included in the zocecium, consequently from the polypide, the muscles, the 

 compensation-sac, etc. The structure of the polypide has up to the present hardly 

 been subject to any comparative study in the Cheilostonutta, and it seems reaso- 

 nable to suppose that .such an investigation of this division, just as in the Cleiw- 

 stoinala, might show differences which would be of importance as distinguishing 

 characters. Thus certain Ctenostome genera (Botverbankia, Vesicularia, Ainatliia), 

 as we know, are remarkable in that they possess a gizzard while the lophophore 

 in Flnslrella in contrast to the condition in Alciionidium, is furnished with a ciliated 

 longitudinal furrow and two vibratory threads. That there are also differences 

 in the structure of the alimentary canal in the Cheiloslomata appears from Busk's 

 observation, that the coecum is absent in Urceolipora nana and Carbasea Moseleiji, 

 the last species of which no doubt also belongs to the family Onchoporidae, in 

 the other members of which we should therefore find possibly the same characters. 

 The parietal muscles in the Clieilostomata may, as is known, appear in difTerent 

 ways. Whilst in the Malacnstega they are attached at one end to the calcareous 

 lateral walls, and at the other to the membranous frontal wall, in the Ascophora 



