NO. 2 OSBURN: eastern pacific BRYOZOA CHEILOSTOMATA 395 



is semilunate, broad, extending across the full width of the front to 

 the lateral pores ; the rostrum considerably elevated, in the midline and 

 directed toward the aperture which it overhangs slightly; the mandible 

 short-triangular and directed upward and backward at an angle of about 

 45 degrees. 



The ovicell is comparatively large, about 26 mm wide, smooth, 

 rounded, prominent and conspicuous ; the peristome is sometimes extended 

 across above the orifice in complete calcification. 



This is a common northern and arctic species, on the Atlantic coast 

 as far south as Cape Cod and along the Pacific coast from Point Barrow, 

 Alaska, to southern California. O'Donoghue listed it from Round Island 

 and Northumberland Channel, British Columbia. 



Hancock Stations: 1224, Newport Harbor channel, and 1067, Santa 

 Barbara Island, southern California, the most southerly localities. Also 

 Tomales Bay, California (R. J. Menzies, collector) ; Middle Bank, 

 Puget Sound, Washington (J. L. Mohr, collector) ; Stations 20-40 and 

 100-40, Alaska Crab Investigation; and Point Barrow, Alaska, Arctic 

 Research Laboratory (G. E. MacGinitie, collector). Shallow water 

 down to 60 fms. 



Porella porifera (Hincks), 1884 

 Plate46, figs. 9-11 



Porella marsupium form porifera Hincks, 1884:24. 

 Porella marsupium var. porifera, O'Donoghue, 1923 :40. 

 Smittina porifera, Canu and Bassler, 1923 :147. 

 Cystisella aviculifera Canu and Bassler, 1923 :152. 

 Smittina marsupium var. porifera, O'Donoghue, 1926:69. 



The zoarium forms small white encrustations on shells and pebbles. 

 The zooecia vary remarkably in size from the center of the colony out- 

 ward, from 0.40 to 0.65 mm in length often in the same colony when 

 free-growing on a plane surface ; width 0.30 to 0.40 mm ; rhomboid to 

 long ovate. The frontal is considerably inflated in young zooecia but 

 may become nearly flat in advanced calcification ; the few areolar pores 

 are sometimes occluded with the thickening of the crust. The primary 

 aperture is a little more than a semicircle, and varies in size with the 

 zooecia, from 0.12 to 0.14 mm in width. The peristome is high and thin, 

 united with the avicularian chamber proximally, lower distally where 

 it bears 4 small evanescent spines ; with complete calcification the frontal 

 on the sides may rise to the top of the peristome and fuse with it. The 

 chamber of the suboral avicularium is considerably inflated and extends 



