74 



family Adeonidae within the division Ascophora, but as a rule together with de- 

 pendent ones. Otherwise they appear very seldom in this division, and are for 

 instance found in Schizoporella spongites, Arthropoma Cecili, var., Schizotbeca fissa and 

 Chorizopora Brongniarti. 



The most important difference in structure, which the heterozocecia present 

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

 between the opercular and the subopercular area. It is namely, except in a few 

 cases, absent in the division Anaska, and, except in the family Adeonidae and 

 Leieschara Crustacea, it is found everywhere in the division Ascophora. The ab- 

 sence of such a transverse bar in ^Lepraliaa Poissoni and in Dorgporella spathuli- 

 fera makes it probable that these forms belong to the division Anaska. On the 

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

 ally taken no real systematic importance, and the same heterozooecium may 

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

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

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

 examples of such a variable development of the two heterozooecial forms. While 

 the heterozocecia within the division Ascophora, where they 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 heterozocecia in the division Anaska, and 

 most of the heterozocecia, which by their peculiarities help to characterize the 

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

 headed avicularia are characteristic of the family Bicellariidae, we find more or 

 less peculiar vibracle forms in the genera Caber ea, Scrupocellaria, Ongchocella, 

 Selenaria, Cupularia and Lunalaria. The avicularia in the family Adeonidae have 

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

 other Ascophora by lacking the above-mentioned transverse bar, but they also 

 show a constant character in the avicularia mandible, which is provided with 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 ocecia, 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 importance is rather diminished by their 

 inconstant appearance I must yet look upon them as some of the most important 

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



