1908] Bohertson. — Incmsting Bryozoa. 255 



Phylum Mom.uscoida Milne-Edwards. 



Class BRYOZOA Ehrenherg. 

 Sub-Class Ectoprocta Nitsche. 



Order GYMNOL.EMATA Allman. 

 Sub-Order I. Chilostomata Busk. 



The first seven families of the Chilostomata, viz., the Aeteidce, 

 Eucratiidce, Cellulariidce, Biccllariidce, Notamiidce, Cellariidw, 

 and Flustridce, have been treated by the writer ( '05) in a former 

 paper. Of the remaining families, representatives of ten occur 

 on the western coast of North America. All of these are incrust- 

 ing at some stage of their growth. A few acquire an erect 

 branching habit but are for the most part non-flexible. A strict 

 division cannot be made among the bryozoa, however, on habit of 

 gro'v^'th, since many species form both incrusting and non-incrust- 

 ing colonies. One family, the Steganoporellidce, included in those 

 here treated, grows in large incrusting colonies covering the stems 

 and fronds of sea weed, but at any point sending up branches 

 which frequently form tangled masses (pi. 17, fig. 27a). These 

 branches, like those of the Cellariidai which they resemble, are 

 furnished at regular intervals with joints composed of aborted, 

 non-calcified zocecia which imj)art to the erect branches more or 

 less flexibility. 



It is difficult, indeed impossible, to characterize each family 

 by a word, or in any very easy, simple way. A little experience, 

 however, soon acquaints one with general characters so that there 

 is usually no difficulty in deciding to what family a given speci- 

 men may belong. The keys which are here furnished are in- 

 tended for the use of beginners and are made as simple as pos- 

 sible. They are purely artificial, and apply only to the bryozoa 

 of the California coast. They may or may not apply to foreign 

 species or to new species which may be hereafter described. 



