394 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



the suboral avicularium. The avicularium chamber extends laterally to 

 the areolar pores on both sides but is completely embedded in and obscured 

 by the thick front which rises even above the avicularium so that the 

 rounded mandible often may be seen only by tilting the specimen. There 

 are no spines and no additional avicularia. 



The ovicell, about 0.24 mm wide, is at first smooth and shining, im- 

 perforate, but soon becomes entirely immersed. 



This species, the genotype of the genus Porella, differs considerably 

 in appearance from most of the other species which are here assigned 

 to Porella because of the rougher frontal surface, but the imperforate 

 frontal and ovicell, the low, small (vestigial or incipient) lyrula and 

 cardelles (often wanting), with a suboral avicularium, appear sufficient 

 to characterize the group. 



The species is northern Atlantic in distribution, extending into the 

 Arctic where it is apparently circumpolar. Earlier records are often 

 questionable as it was confused with Smittina (Millepora) cervicornis 

 (Pallas), which has a perforated frontal and which is more southern in 

 distribution. In the Pacific it has not been reported, but at Point Barrow, 

 Alaska, Prof. G. E. MacGinitie has dredged large foliate specimens 

 (Arctic Research Laboratory). 



Porella acutirostris Smitt, 1867 

 Plate 46, fig, 4 



Porella acutirostris Smitt, 1867:21 and 132. 



Porella major Hincks, 1884:51. 



Porella acutirostris. Waters, 1900 :83. 



Porella acutirostris, Osburn, 1912 :248 ; 1923 : 1 ID. 



Porella acutirostris, O'Donoghue, 1923 :41. 



Zoarium encrusting on stones and shells, usually in the form of white 

 rounded colonies. The zooecia are elongate-ovate and usually regularly 

 disposed in radiating series, the frontal evenly convex and smooth or 

 slightly granulated, with a row of small areolar pores which often 

 become occluded in later calcification. (Zooecial length 0.45 to 0.60 mm, 

 width 0.30 to 0.45 mm.) The primary aperture is rounded distally, 

 straight on the proximal border with a small, short (often scarcely 

 noticeable) lyrula, or none, and the cardelles are minute and incon- 

 spicuous or wanting. The peristome is high and thin, connected with 

 the sides of the avicularian rostrum but not enclosing it ; when an ovicell 

 is present the peristome is connected with it. The avicularian chamber 



