NO. 2 OSBURN: eastern pacific BRYOZOA — CHEILOSTOMATA 417 



(Not "Porella collifera Robertson," Canu and Bassler, 1923 :148.) 



Zoarium encrusting, the secondary layers often rough and nodulous. 

 Zooecia of moderate size, averaging about 0.50 mm long (range 0.40 

 to 0.65 mm), the width between 0.30 and 0.40 mm. In the primary 

 layer the zooecia are regularly disposed in quincunx, the form ovate or 

 elongate-hexagonal ; the frontal is a coarsely granulated pleurocyst, with 

 moderately large areolar pores and usually a few additional pores (espec- 

 ially near the proximal end). The extra frontal pores often give the 

 appearance of a tremocyst, but this is nullified by their occasional com- 

 plete absence, and in young zooecia the pleurocyst may be observed to 

 develop from the zooecial borders above the olocyst. The frontal prom- 

 inences or colli (hills) which characterize the species are often but little 

 developed on the primary layer, usually 1 to 3 small but rather high, 

 erect knobs, but in later growth the tubercles may be broad and heavy 

 and sometimes nearly cover the front. 



The primary aperture is nearly round, slightly longer than broad 

 (0.16 mm long by 0.15 mm wide), with strong cardelles and a moderate 

 lyrula which is considerably wider at its base and truncate at the tip. 

 The peristome is thin and little elevated, sometimes forming a secondary 

 sinus on the proximal border but always leaving the lyrula and aperture 

 well exposed ; 2 long spines are present on the distal border in young 

 zooecia. The avicularia are of three kinds : ( 1 ) small to large, semi-erect, 

 with a triangular mandible directed distally, located proximal to and 

 usually at one side of the peristome; (2) small ovate avicularia variously 

 situated on the front or replacing the triangular ones beside the aperture; 

 (3) rarely an elongate-spatulate avicularium replacing an oval one on 

 the frontal. 



The ovicell is large, 0.25 to 0.30 mm in width, rounded and con- 

 spicuous, with several (6 to 8) large pores which vary in size, form 

 and disposition ; with complete calcification the ooecial cover often be- 

 comes very rough, with protuberances similar to those on the frontal. 



This species is evidently a member of the S. trispinosa group, but it 

 is differentiated by its larger size, especially of the primary aperture, 

 and by the conspicuous erect frontal nodules or protuberances. Described 

 from the Coronado Islands, Mexico, a little south of the harbor of 

 San Diego, California, which appears to be about its southern limit. 

 O'Donoghue listed it from numerous localities in British Columbia. 



Hancock Stations : dredged at numerous localities from Oregon south 

 to the islands o£E the coast of southern California; common also at 

 various shore stations. 



