NO. 2 OSBURN: eastern pacific BRYOZOA CHEILOSTOMATA 375 



Family Microporellidae Hincks, 1880 



The most important character is a small median pore, the ascopore, 

 at a little distance proximal to the aperture. It is the outlet of the ascus 

 or compensation sac, and varies in form and position in the different 

 species, and it may also show considerable variation with different de- 

 degrees of calcification. The aperture is nearly straight on the proximal 

 border, and the operculum is simple, having no extension proximal to 

 the cardelles. Spines are present on the peristome and avicularia are 

 present in the genus Microporella. The frontal is a tremocyst. Dietellae 

 present. The ovicell is hyperstomial and closed by the operculum. 



Genus MICROPORELLA Hincks 1877 



The aperture is semicircular, straight on the proximal border. The 

 ascopore is semilunar or round and is situated rather close to the aper- 

 ture so that there are no tremopores between. Pointed avicularia are 

 present in various positions. Genotype, Eschara ciliata Pallas, 1766. 



The question of what is a "good species" rises again and again in 

 this genus, as most of the differential characters are subject to variation. 

 The avicularia differ in position, alongside or slightly distal to the asco- 

 pore, or on the front proximal to it ; in the latter case they are usually 

 more lateral in position. There is some variation, however, in some of 

 the species, as in ciliata where occasionally an avicularium may be found 

 beside the ascopore. The number is of some importance, whether single 

 or paired, but again those with a single avicularium may occasionally 

 have two and those which ordinarily are paired may have only one. The 

 form of the mandible also varies within the species, and species with 

 long-triangular mandibles may have them more or less setose, even 

 within the same colony. The form of the aperture varies in the different 

 species from semicircular to considerably more than a semicircle, and 

 the same colony may show some variation; also the proximal border 

 may or may not bear small hinge teeth. The umbos in some are heavily 

 developed, in others they are smaller and in still others they may be 

 evident only occasionally. The ovicell offers little of importance, though 

 in some forms it is developed around the aperture farther than in others, 

 in some it bears a collar around the orifice, and in some cases the size 

 is useful. The size and number of the spines have been made use of, but 

 here the variation, especially in size, is very great. 



