NO. 2 OSBURN: eastern pacific BRYOZOA CHEILOSTOMATA 379 



from the Pleistocene of Santa Barbara, Santa Monica and San Pedro, 

 California, 



Hancock Stations: 1232-41, San Pedro, and 1300-41, Santa Cruz 

 Island, California. Also from Dillon Beach, California (Menzies, 

 collector). Shallow water to 56 fms. 



Microporella vibraculifera (Hincks), 1884 

 Plate 44, fig. 7 



Microporella ctliata form vibraculifera Hincks, 1884:15. 



Microporella ciliata var. vibraculifera, O'Donoghue, 1923 :31 ; 1926:64. 



Microporella vibraculifera, Canu and Bassler, 1923:124. 



There is much general resemblance of this species to ciliata, but it is 

 larger in all dimensions, coarser in appearance, and the avicularium is 

 strikingly different. 



The zoarium is encrusting on shells, stones and coarser algae. The 

 zooecia are irregularly elongate hexagonal, 0.50 to 0.60 mm long by 

 0.34 to 0.40 mm wide, a little inflated, the frontal with large tremopores 

 when the smooth shining ectocyst is removed. The aperture is semicircular 

 with the proximal corners a little rounded, the proximal border straight 

 and with no evidence of cardelles, 0.09 mm long by 0.13 mm wide. The 

 peristome is thin, a little elevated and provided with 5 to 7 stout spines. 

 The ascopore, as in ciliata, is reduced to a lunate slit by the development 

 of the shelf on the proximal border ; the rim of the pore is very slightly 

 elevated. The avicularium, comparatively, is of giant proportions, its 

 chamber usually extending laterally over more than half the width of the 

 front and elevated on its proximal side so that it appears to be tipped 

 forward ; there is a very heavy pivot ; the setose mandibles, which may 

 be 1.00 mm or more in length, are grooved on the under surface for 

 their entire length, with a pair of minute hooks near the base, and are 

 directed more or less sideways. There is no diflSculty in identifying the 

 species when the mandibles are present and even when these are denuded 

 the size and position of the avicularian base, with its unusually strong 

 hinge bar, easily distinguish it. 



The ovicell is large, 0.35 to 0.40 mm wide, smooth or slightly 

 umbonate, ribbed around the base and usually with a thick, raised collar 

 around its aperture. 



Described by Hincks from British Columbia, "Queen Charlotte 

 Islands," and listed by O'Donoghue without special data. Canu and 

 Bassler record it from the Pleistocene of San Pedro, Santa Monica 

 and Santa Barbara, southern California. 



