215 



the genus Clauiporella the proximal one is also represented by a single rosette- 

 plate. While the proximal group serves as a communication with the pedal 

 chamber the distal group serves either as communication with the scapular 

 chamber only as in Scuticella plagiostoma, Sc. intermedia, Sc. ventricosa. Cat. 

 margaritacea, or as communication with the infra-scapular chamber as well, e. g. 

 Sc. amphora, Sc. lorica, Sc. Wilsoni and the species of the genus Catenaria. If the 

 scapular chamber is developed into an avicularium, its roof or distal wall (PI. XI. 

 figs. 1 c, 3 b, 3 c, 4 b) is furnished with a number of rosette-plates forming a 

 communication with the supra-scapular chamber, while the proximal wall fur- 

 nished in the same way (PI. XI, figs. 1 c, 2 b, 3 a, 7 b) makes a septum for the 

 infra-scapular chamber, which, as stated above, in a series of species may also 

 be in direct communication with the zooecium. If on the other hand the scapular 

 chamber has not attained this degree of development it will coalesce with or be 

 only incompletely separated from the adjacent chambers. While as a rule there 

 will be no difficulty in distinguishing the various lateral chambers belonging to 

 the solitary zooecia or those belonging to the outer (abzocEcial) sides of the bi- 

 zooecial articulate parts, it may be more difficult to identify several of the lateral 

 chambers belonging to the inner (adzooecial) sides of the two zooecia in a bi- 

 zooecial segment. Moreover these two zooecia are not of equal value, as we must 

 distinguish between a mother-zooecium springing from the proximally situated 

 segment, and a daughter-zooecium without communication with the segment but 

 issuing from the mother-zooecium. 



If the adzooecial side of the daughter-zooecium is furnished with an avicula- 

 rium, its three distal lateral spaces will always be clearly developed, e. g. in 

 Costicella hastata (PI. XX, fig. 8 b), Pterocella alata (PI. XXI, fig. 4 a), Catenaria 

 elegans (PI. XXI, fig. 2 a) and Cat. formosa (PI. XXI, fig. 3 a), whereas its pedal 

 lateral chamber (d. IV) is usually wanting. It is however present in all the spec- 

 ies of the genera Costicella and Catenaria, in Strophipora Harvegi as well as in 

 Scuticella sacculata. Busk and Sc. frigida, Waters ^ which two species may be 

 regarded as transitional forms between the genera Scuticella and Catenaria. Al- 

 though the daughter-zooecium itself has lateral chambers it still takes the 

 same place in relation to the mother-zooecium as the scapular chamber in a 

 solitary zooecium, being in communication with the mother-zooecium through the 

 group of rosette-plates described above as the distal, and the adzooecial, distal 

 lateral chamber of the mother-zooecium which communicates with the daughter- 

 zooecium through a group of rosette-plates, must accordingly be explained as the 



» 115, pi. 1, fig. la, 



