272 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



As a rule the species are more heavily calcified than in the Anasca. 

 The frontal is primarily an olocyst, which is probably merely the com- 

 pleted extension of the anascan g>TOnocyst. In most cases an additional 

 calcified layer is laid down on top of the olocyst, either a pleurocyst which 

 grows inward toward the center of the front from the marginal pores 

 or areolae, or a tremocyst which develops evenly over the olocyst from 

 the numerous scattered tremopores which perforate the frontal wall. 

 Oral spines are frequently present ; also avicularia which may be either 

 interzooecial (vicarious) or frontal (dependent). The zoaria are usually 

 encrusting, but not infrequently rise into folds, nodules, or stems. The 

 latter may be branched and are sometimes provided with chitinous joints. 

 The ovicells in most cases are hyperstomial, opening above the primary 

 distal rim of the aperture, or they may be endozooecial and formed by 

 the distal extension of the zooecial cavity and opening below the level 

 of the operculum ; in a few genera ovicells appear to be entirely absent, 

 the larvae developing within the zooecial cavity. 



The Ascophora are a dominant group of the recent Bryozoa, occurring 

 everywhere in the seas and are of some importance as nuisance organisms 

 in the encrusting of ship's bottoms, buoys, etc., or covering the "cultch" 

 of oyster beds to the exclusion of oyster larvae. While the individual 

 zooecia rarely are more than a millimeter in length the colonies often 

 reach considerable size. Budding may be terminal, lateral or frontal and 

 in the latter case new layers may grovi^ over the older ones to form very 

 thick encrustations. The writer has counted more than 30 layers in 

 species of Smittina. 



They are distributed from the polar seas to the equator and from 

 shore to great depths. A few species are estuarine in water of low salinity 

 but none of them have been able to become adapted to pure fresh water. 

 They are abundant as fossils from the Cretaceous onward since the thick 

 calcareous walls are readily preserved in bottom deposits. Many of the 

 earlier genera no longer exist, but more than 100 of those known as 

 fossils are still living and about the same number are known only as 

 Recent genera. As research continues these figures will undoubtedly be 

 greatly altered. The present work includes several genera now living 

 but hitherto known only as fossils and a few in which the reverse is true. 

 Evidently the bryozoan fauna of the Pleistocene differed very little in 

 Its general aspects from that of the present. The Ascophora do not appear 

 to be a decadent group. 



It appears impossible with our present lack of knowledge, to arrange 

 the families of the Ascophora in any logical evolutionary order. Certain 

 families appear to be simpler than others, that is, they seem to have 



