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adzooecial, supra-scapular (m. I) lateral chamber of the mother-zocecium. This is 

 clearly seen e. g. in Scuticella maculata (PI. XX, fig. 5 b), in which species this 

 chamber lies opposite the corresponding abzocecial, supra-scapular lateral chamber, 

 from which it is only separated by a short raised line. Although the daughter- 

 zooecium, as said before, may be considered the adzooecial, scapular chamber of 

 the mother-zooecium, and we cannot for this reason expect to find an avicularium 

 on the adzooecial side of the mother-zooecium, the species of the genus Pterocella 

 (PI. XXI, fig. 4 a) make an exception to the rule, a small adzooecial avicularium 

 being always present. The adzooecial, pedal chamber of the mother-zocecium 

 (m. IV), which is always developed, is not difficult to find, and it then only 

 remains to determine the adzooecial, infra-scapular chamber of the mother-zooe- 

 cium (m. III). We have seen that an infra-scapular chamber is only independently 

 developed in such zooecia as are furnished with an avicularium with which they 

 communicate through the proximal wall of the latter, but that in a series of spe- 

 cies it also communicates with the zocecium itself through some of the rosette- 

 plates in the distal group. In accordance with our conception of the daughter- 

 zooecium as being the scapular chamber of the mother-zooecium, we must consider 

 the only lateral chamber that we have not yet explained as the adzooecial, infra- 

 scapular chamber of the mother-zocecium. It is in most cases a very small, oval 

 or pear-shaped, sometimes almost slit-like space, situated almost in the middle 

 of the boundarj' line between the two zooecia of the segment, and rarely attain- 

 ing any considerable size. Its extent is largest in Strophipora Harveyi (PI. XXI, 

 fig. 6 a), in which besides extending a little into the daughter-zooecium it also 

 occupies half the frontal surface of the mother-zocecium. In Scuticella Wilsoni it 

 also attains a considerable size, filling as it does the greater part of the deep 

 depression between the sternal areas of the mother-zooecium and the daughter- 

 zooecium. In the species of the genus Catenaria this boundary chamber has like 

 the ordinary infrascapular chamber a double inner communication (through ro- 

 sette-plates), viz. both with the daughter-zooecium and with the mother-zooecium, 

 while the corresponding chamber in Scuticella species only communicates with 

 the mother-zocecium. A similar difference, as already mentioned, is found within 

 the genus Scuticella, all the rosette-plates of the distal group serving in some 

 species as a communication with the scapular chamber, while in others some of 

 them form a communication with the infrascapular one. With respect to the 

 above chamber we must still notice that it generally occurs somewhat incon- 

 stantly within the genus, in Scuticella margaritacea for instance it is absent, while 

 it is present in the form described in this work under the name of Sc. mar- 

 garitacea, var. connectens (PI. XX, fig. 3 b), but which perhaps ought to be con- 



