NO. 2 OSBURN: eastern pacific BRYOZOA — CHEILOSTOMATA 507 



Gostazia robertsoniae Canu and Bassler, 1923 

 Plate 62, figs. 1-2 



Costazzia robertsoniae Canu and Bassler, 1923 :181. 

 Cellepora costazi, Robertson, 1908 :313, in part. 

 Cellepora costazii, O'Donoghue, 1923 :48, in part. 



The zoarium encrusts small stems, sometimes forming only irregular 

 nodules but often giving off erect branches, irregularly forked, to a 

 height of 30 mm or more ; the branches are from 2 to 4 mm or more in 

 diameter ; occasionally encrusting on flat surfaces. The zooecia are more 

 or less decumbent at the growing edges, but erect or nearly so in the 

 secondary layers; moderately large, about 0.40 mm in width and the 

 marginal ones about 0.65 mm in length. The frontal is roughened as in 

 costazia, with a few pores in addition to the areolar ones, in advancing 

 calcification carried upward on the frontal, and those near the distal 

 end carried upward around the peristome. The primary aperture is a 

 little elongate, about 0.18 by 0.14 mm, rounded distally, slightly nar- 

 rower proximally and with a distinctly v-shaped sinus. The peristome 

 is moderately high, with the usual pair of lateral-oral small pedicellate 

 avicularia and a third similar median avicularium (rarely two) on 

 the distal border in the absence of an ovicell; the latter type is often 

 wanting but I have never found it entirely absent from any colony. 

 Broadly spatulate or oval interzooecial avicularia are sometimes present, 

 with a complete pivot. 



The ovicell is attached lower on the peristome than in costazii and 

 is much more readily embedded by later calcification, 0.26 to 0.30 mm 

 wide and broader than long, the ectooecium smooth and shining, the 

 semicircular frontal area with triangular radiating pores, which may 

 eventually be occluded by the overgrowth of the ectooecium. The peri- 

 stome sometimes forms a narrow cross-bar immediately above the orifice, 

 but the area always retains its lunate form. 



The species was described from the Pleistocene of Santa Monica, 

 California. The original description is wanting in some respects, especially 

 in the failure to note the median distal avicularium. A specimen from 

 the type locality, presented to me by Dr. R. S. Bassler shows this 

 character, and abundant fossil and recent material in the Hancock col- 

 lections and those of the Los Angeles County Museum prove the identity 

 of the Pleistocene and recent specimens. 



It is the most common species of the genus in the waters of Cali- 

 fornia, dredged at 9 stations among the Channel Islands and shorewise 



