NO. 2 OSBURN: eastern pacific BRYOZOA CHEILOSTOMATA 299 



areolar pores between which are short conspicuous costae which extend 

 to the base of the avicularian chamber. The disto-central area is occupied 

 by a large, rounded avicularian chamber which rises in the form of a 

 central umbo; the rounded avicularium is conspicuous, set at an angle 

 of about 45 degrees to the plane of the aperture. In older, ovicelled 

 specimens there are occasional frontal avicularia similar to the usual 

 suboral ones. The peristome is low and thin ; in one very young specimen 

 there are 2 or 3 small distal oral spines. The aperture is rounded, usually 

 a little broader than long and straighter on the proximal border, varying 

 considerably in size and form, averaging about 0.30 mm wide by 0.26 mm 

 long. 



The ovicell is large, about 0.45 mm wide by 0.40 mm long, high and 

 rounded, rough except at the center of the front. 



There are very few references to U. patens; Smitt described it 

 from Spitsbergen and Nordgaard knew it only from that area. Other- 

 wise there appear to be no records under that name, but it is more 

 than probable that the two references to U. verrucosa from Greenland 

 refer rather to patens. The differences are not great, but Nordgaard 

 has pointed out that in patens the costules on the front are shorter and 

 smaller and the mandible of the avicularium is slanted backward from 

 the aperture and exposed to view. Hastings adds that it differs "in the 

 form of avicularian chamber, which is larger and more oval in outline, 

 extending further towards the proximal end of the zooecium." Also 

 the wing-like processes of the frontal at the sides of the aperture are 

 wanting. 



Point Barrow, Alaska, Arctic Research Laboratory, Prof. G. E. 

 MacGinitie, collector, several colonies, 7 to 15 fms. 



Umbonula arctica (Sars), 1851 

 Plate 36, fig. 6 



Lepralia arctica Sars, 1851 :149. 

 Eschara pavonella Alder, 1864:106. 

 Discopora pavonella, Smitt, 1867:28. 

 Mucronella pavonella, Hincks, 1880:376. 

 Mucronella pavonella, Robertson, 1908:308. 

 Mucronella pavonella, O'Donoghue, 1923:46; 1926:71. 

 Discopora arctica, Nordgaard, 1918:79. 

 Umbonula arctica, Hastings, 1944:282. 



Zoarium encrusting, sometimes rising into bilaminate folds. The 

 zooecia are moderately large, very variable, averaging about 0.60 mm 



