THE MOUNT DESERT KEGION 341 



The zoarium forms reddish-browii incrustations. The zoo- 

 ecia are large, distinctly separated, the front somewhat in- 

 flated, granular, and with a row of marginal pores (seen after 

 calcining). The aperture is quite simple, rounded distally, 

 without hinge denticles, and with a single sharp median spine 

 on the proximal border. There is no peristome, and avicularia 

 and spines (other than the median tooth) are wanting. The 

 ooecium is hemispherical, inconspicuous, and subimmersed. 

 The frontal wall is thick, and this, with the great simplicity 

 of the zooecium and the presence of the single short spine-like 

 denticle on the oral border, will easily distinguish it from any 

 other species in our fauna. 



Hincks described it in the genus Mucronella, but later (1892, 

 p. 152) removed it to MoiwporeUa. As the latter genus is 

 understood at present, spinulifera cannot possibly belong in it. 

 It is possible that it may not belong in Mucronella, but I leave 

 it there for the present, as my material is too scanty for 

 more than the determination of the species. 



Umbonula Hincks, 1880 



Umbonula arctica (Sars), 1851. PL 11, fig. 7. (Osburn, 

 1912, p. 243 (Mucronella pavonella), for references; Whit- 

 eaves, 1901, p. 107 {Mucronella pavonella), Canadian rec- 

 ords.) Occasionally taken, thirteen dredging stations, not 

 found at shore stations. Found in great numbers on a sunken 

 spruce tree which was pulled up from a depth of 85 feet at 

 station 13. The species is common in the Arctic and North 

 Atlantic and as far south as Cape Cod. 



The zoarium forms rounded or fan-like incrustations on 

 stones and shells and often projects, shelf -like, from the stems 

 of hydroids and other bryozoans. The zooecia are large and 

 broad, regularly arranged, areolated around the margin, with 

 ribs extending toward the center. The aperture is large, 

 nearly round, with a small triangular tooth on the middle 

 of the proximal border. A small oval avicularium on either 

 side of the aperture. Ooecia wanting. 



