NO. 2 OSBURN: eastern pacific BRYOZOA CHEILOSTOMATA 393 



Key to the Species of Porella 



1. Zooecia large, the frontal more or less costate, no cardelles, no 



spines compressa 



Zooecia of moderate size, slightly or not at all costate .... 2 



2. No oral spines, avicularian mandible pointed .... acutirostris 

 Small oral spines (2 to 4), mandible not sharp-pointed .... 3 



3. Avicularian chamber large and prominent, with 2 to 6 



pores porifera 



Avicularian chamber smaller and less prominent, pores usually 

 wanting 4 



4. Peristome flaring, especially at the proximal end, no lyrula, 4 small 



evanescent spines patens 



The secondary aperture is pyriform, the avicularium projecting 

 over the aperture 5 



5. Zooecia distinct only when young, ovicell becoming completely 



embedded concinna 



Zooecia remaining distinct, ovicell marginated around the base, 

 lightly striated columbiana 



Porella compressa (Sowerby), 1805 

 Plate 46, figs. 1-3 



Millepora compressa Sowerby, 1805 :83. 

 Eschara cervicornis. Busk, 1854:92. 

 Porella compressa, Hincks, 1880:330. 



The zoarium is erect, bilaminate and branching or flabellate and 

 contorted, arising from an encrusting base to a height of 50 mm. The 

 zooecia are large, averaging about 0.70 mm long, but varying from 0.60 

 to 1.00 mm, and the width ranges usually between 0.40 and 0.50 mm. 

 The frontal, which is only slightly swollen, is a granular pleurocyst 

 with a row of numerous and well-marked areolar pores and occasionally 

 some additional scattered similar pores near the proximal end ; between 

 the areolar pores narrow costal ridges run toward the center ; a slightly 

 raised line usually separates the zooecia. The primary aperture is large, 

 about 0.20 mm wide by 0.16 mm long, rounded distally and on the sides, 

 straight on the proximal border where there is a very low lyrula which 

 is nearly as wide as the aperture and which usually cannot be observed 

 except from the inner view of the frontal ; cardelles appear to be entirely 

 wanting. The secondary aperture is more or less pyriform, the high, 

 thin peristome rising slightly above the thick frontal wall and enclosing 



