NO. 2 OSBURN: EASTERN PACIFIC BRYOZOA CHEILOSTOMATA 505 



The zooecia are usually erected, sometimes more or less procumbent 

 especially at the growing edges; the frontal imperforate in the central 

 area, with one or more rows of areolar pores which usually are carried 

 upward by later calcification to the base or sometimes nearly to the top 

 of the peristome; the primary aperture bears a distinct sinus, usually 

 somewhat v-shaped ; there is a pair of small lateral oral avicularia which 

 usually rise above the level of the peristome. The ovicell is prominent, 

 opening into the peristomial cavity above the level of the primary aper- 

 ture and not closed by the operculum; it always bears a semicircular 

 frontal area which is bordered with radiately arranged pores separated 

 by small ribs, though a few more central pores may also occasionally be 

 present; in advanced stages of calcification this area sometimes becomes 

 covered. 



The species of Lagenipora often resemble those of Costazia but 

 the frontal is a tremocyst with the pores distributed over the whole 

 surface and the semicular area of the ovicell has smaller and more 

 numerous pores without radial arrangement. 



Key to the Species of Costazia 



1. Zoarium encrusting, or if erect the branches are stout .... 2 

 Zoarium erect with slender, cylindrical branches ; the sinus of the 



aperture semicircular procumbens 



2. Zoarium rough, encrusting and nodular, or erect with terete stout 



branches; zooecia coarse 3 



Zoarium smaller and neater in appearance, usually pisiform on 

 small stems 4 



3. Usually encrusting, the coarsest of our species; aperture with a 



deep V-shaped sinus ventricosa 



Erect from a small base, with rounded irregular branches; the 

 sinus small and shallow surcularis 



4. A distal median oral avicularium in addition to the lateral ones; 



sinus deep robertsoniae 



Only the lateral oral avicularia present 5 



5. Sinus deep ; frontal area of ovicell lunate costazi 



Sinus small and shallow ; frontal area of ovicell rounded ; arctic 



species nordenskjoldi 



