NO. 2 OSBURN: eastern pacific BRYOZOA — CHEILOSTOMATA 413 



also possible that more careful analysis would show further distinctions 

 in various parts of the world. Most of the varieties have been based on 

 the form, size and distribution of the avicularia and the height and form 

 of the peristome and no one can deny the variability of these structures 

 in P. trispinosa, but the size and form of the primary aperture, the char- 

 acters of the operculum, lyrula, cardelles, ooecium, etc., have usually 

 been neglected. In all of the numerous specimens similar to trispinosa on 

 the Pacific coast, from Alaska to the Galapagos, which have come under 

 my observation, none are exactly like those from western Europe. The 

 nearest approach to identity is among the northern specimens, from Alaska 

 to British Columbia. Farther south the peristome is usually lower and 

 less spout-like and the aperture somewhat larger. The avicularia near 

 the peristome also are usually much larger than in the northern specimens. 



The zoarium is encrusting, often becoming multilaminate and nodular 

 or even erected in low folds. The zooecia are moderate in size, 0.45 to 

 0.60 mm long by about 0.30 mm wide, but varying greatly in both size 

 and form ; the primary layer growing on a flat surface is quite regular 

 with the zooecia in parallel series, but in the secondary layers they may 

 be turned in all directions ; distinct only in younger growth stages which 

 often are slightly ventricose and have raised separating lines. The frontal 

 is a pleurocyst, granular or irregularly roughened, with a row of areolar 

 pores (occasionally a few additional pores). The primary aperture in 

 marginal zooecia averages 0.11 mm in width by 0.10 mm in length, 

 rounded except on the proximal border where there is a moderately devel- 

 oped lyrula ; the condyles small. The peristome is thin, high on the prox- 

 imal border where it is often somewhat notched, sloping downward on the 

 sides and wanting on the distal border where there are 3 (2 to 4) spines; 

 the overhang of the peristome usually obscures the lyrula and condyles. 

 The avicularia are variable; the most characteristic type is moderately 

 large, located a little proximal and to one side of the peristome, the long- 

 triangular rostrum elevated and directed more or less distally beside the 

 peristome, there is much variation in the size ; frequently there are other 

 avicularia, varying in size and form distributed irregularly over the 

 frontal. 



Ovicell prominent, the frontal surface usually a little flattened, with 

 moderately large pores that vary in size and form ; width 0.26 mm ; in 

 full calcification the front often becomes rough and the ovicell much 

 embedded. 



The above description applies to more northern and English speci- 

 mens ; farther south on the Pacific coast there are minor differences, such 

 as : the aperture is slightly larger ; the giant avicularia are usually larger 



