74 



laiiiily Adeoniildf williiii llic division Ascoiiliora, l)iil ns a rule together with de- 

 pendent ones. Othei'wise they :ij)pear very seldom in this division, and are for 

 instance found in Schizoporclld sixukjUcs. Arlhicjioiud C.ecili, var., Schizothecci fissn and 

 Chorizoponi BrniKju uiiii. 



The most important dilTerenee in slrueture, whieh the heterozotreia present 

 in systematic regard is the presence or absence of a calcareous transverse bar 

 between the o|)ercular and the subopercular area. It is namely, except in a lew 

 cases, absent in the division Aiuiska, and, except in the family Adeonidac and 

 LeieHchura crnslacea, it is found everywhere in the division Ascophoni. The ab- 

 sence of such a transvei'se bar in '■Lepr(ili<i« Poissoni and in Doriiporclhi sjHilhiili- 

 fcra makes it j)robal)]e that these forms belong to the division Anaska. On the 

 contrary the difference between the avicularium and the vibracnium, has gener- 

 ally taken no real systematic importance, and the same heterozott'ciuni may 

 appear in the same genus, even occasionally in the same species, sometimes as 

 an avicularium, sometimes as a \ibraculum. This is the case e. g. in Microporella 

 ciliata, and the genus Microporella as well as the genus Escluirina may serve as 

 examj)les of such a variable develo|)ment of the two heterozoa>cial forms. While 

 the hcterozod'cia within the division Ascophora, where Ihej' are mostly developed 

 as avicularia, only very seldom show so great a modification in their structure 

 that it can be used by the separation of families and genera, there is a much 

 larger diversity in the structure of the heterozorecia in the division Anaskti, and 

 most of the heterozooecia, which by their {)eculiarities help to characterize the 

 families and genera, are vibracles. While the peculiar, freely moveable, bird- 

 headed avicularia are characteristic of the family IVuellnriidac, we lind more or 

 less peculiar vibracle forms in the genera Caberca, Scrupocellaria, Oiujclwcella, 

 Selei}(iri<t, Cupularut and Liuiul(iri<i. The avicularia in the family Aileanidae have 

 a great systematic interest, as they not only differ from the avicularia in all 

 other Ascoj)lior(t by lacking the above-mentioned transverse bar, but they also 

 show a constant character in the avicularia mandible, which is provided wilh a 

 muscular process on each side at the proximal part. The occlusor muscles may 

 also present differences, as they are as a rule double, more seldom single, and 

 this is just the case in the Adeonidae. 



The ooecia, as we have already noticed, appear in a series of widely different 

 types, of which again a single one (the hyperstomial) shows fairly considerable 

 modifications. Although their systematic imj)ortancc is rather diminished by their 

 inconstant apj)earance I must yet look upon them as some of the most im{)orlant 

 formations in systematic regard, and there is no doid)t that they are far more im- 



