NO. 2 OSBURN: eastern pacific BRYOZOA CHEILOSTOMATA 333 



age. The aperture is nearly round, with a broad, shallow sinus. The 

 operculum is well chitinized, yellowish, with muscle attachments re- 

 moved from the border. The peristome is slightly raised, thin, and 

 sometimes connects with the suboral avicularian chamber. The avicu- 

 larium varies in size and location, usually close to the border but 

 often a little removed from it, and the mandible semicircular to very 

 short spatulate. 



The ovicell is large, 0.40 mm wide, the front considerably depressed, 

 perforated by rather large pores. 



As shown by Nordgaard (1918:28) Smitt confused no less than 

 five species in his Escharella poriferdj the "form typica" being the present 

 one. The species, as limited, has been placed under several other genera, 

 Lepralia, Smittina, Schizoporella, but the characters, except for the large 

 size, appear to conform to the genus Schizomavella; the nature of the 

 aperture and operculum, the depressed frontal area of the ovicell and 

 the character of median suboral avicularium. 



It is a high northern species, known from Nova Zembla to Green- 

 land, but the confusion with other species makes it impossible to cite 

 references except where authors have noted the form of the aperture 

 without a lyrula. 



Point Barrow, Alaska, Arctic Research Laboratory, G. E. Mac- 

 Ginitie, collector, 14 fms. 



Genus ARTHROPOMA Levinsen, 1909 



The frontal is a smooth tremocyst with numerous small pores ; aper- 

 ture semicircular, straight on the proximal border, with a narrow slit- 

 like sinus; peristome inconspicuous. The operculum bears a tongue- 

 shaped appendage which fills the sinus. Genotype, F lustra cecilii Audouin, 

 1826. 



Arthropoma cecili (Audouin), 1826 

 Plate 38, figs. 1-3 



Schizoporella cecilii, Hincks, 1884:17. 

 Schizoporella cecilii, Robertson, 1908:288. 

 Schizoporella cecilii, O'Donoghue, 1923 :35. 

 Arthropoma cecilii, O'Donoghue, 1926:58. 



Zoarium encrusting, forming thin, smooth, white layers. Zooecia 

 moderately large, 0.65 to 0.75 mm long by 0.50 to 0.65 mm wide, hex- 

 agonal, distinct with well-marked grooves ; the frontal is a smooth tremo- 



