NO. 2 OSBURN: eastern pacific BRYOZOA CHEILOSTOMATA 273 



undergone less modification from anascan ancestors, but we still have 

 no certain information concerning the origin of the Ascophora. In several 

 of the anascan families, especially the cribrimorphs, a more or less 

 complete cover, the pericyst, has been developed. The ancestors of the 

 Ascophora may have evolved from one of these, but which one is still 

 in doubt, and there is some evidence that there may have been parallel 

 evolution from more than one anascan type of progenitor. 



The arrangement of the families in the present work follows that of 

 Bassler in the Fossilium Catalogus merely for the sake of convenience. 

 When our knowledge of relationships is more complete this arrangement 

 may suffer many changes. This is true also of the genera within a family 

 as certain of the "families" are admittedly merely "catch-alls" which 

 include genera of uncertain relationship. Truly there is much to be 

 learned before the taxonomy of the Ascophora arrives at a settled basis. 



Owing to the heavy calcification the Ascophora are especially difficult 

 to work with. Ordinarily the polypides have been neglected, but by 

 careful decalcification of the skeleton, and staining, many of the details 

 of the soft parts may be observed. The chitinous appendages, opercula 

 and avicularian mandibles, are often of great value in the determination 

 of species and of generic and family relationships. It is possible, by very 

 careful dissection to remove these individually, but it is much easier and 

 usually just as satisfactory to crush a small portion of a zoarium on a 

 glass slide, add a drop of absolute alcohol and mount in clarite or some 

 similar medium. 



For the study of the skeletal details it is frequently necessary to 

 remove the chitinous ectocyst. Treatment with "Javelle water" (eau de 

 Javelle) will remove all the chitinous and soft parts and leave beautiful 

 preparations, but it is much quicker and usually just as satisfactory to 

 burn away the organic matter by the use of the mineralogist's blow-pipe. 

 The technique is very simple — place a small part of a colony on a spatula 

 and with the blow-pipe direct the flame from an alcohol lamp on the 

 specimen. A little experience will indicate when to stop the incineration. 

 Details of the surface, the arrangement of pores, the presence and nature 

 of cardelles and lyrulae within the aperture, the nature of the avicularian 

 rostrum and pivot or hinge denticles, etc., are usually clearly presented 

 by this method. The communication pores, in the side walls, septulae 

 and dietellae, and the nature of the frontal, olocyst, pleurocyst or tremo- 

 cyst, also are more readily observed. A word of caution is necessary, for 

 overheating may destroy a specimen. Unique specimens naturally should 

 never be incinerated unless small fragments can be removed for the 

 purpose. 



