346 BIOLOGICAL SURVEY OF 



size, convex, smooth, or granular, with a row of marginal 

 pores. Primary aperture round in front, straight on the 

 proximal border, the secondary aperture formed by the high 

 thin peristome, which runs forward upon the ooecium to form 

 a conspicuous frontal border; posteriorly the fold extends 

 backward to join with the sides of the rostrum, but not to 

 enclose it. The suboral avicularium has a bluntly triangular 

 (sometimes short oval) mandible and is mounted on a rather 

 high smooth rostrum. The ooecium is large, prominent, 

 globose, smooth, and imperforate. 



PoRELLA PROBosciDEA Hiiicks, 1888. PL 10, fig. 9. (Osburn, 

 1912, p. 249, synonymy and references ; 1912 a, p. 285, Lab- 

 rador and Cape Sable, Nova Scotia ; Whiteaves, 1901, p. 103, 

 Gulf of St. Lawrence.) The most abundant Porella of the 

 region, encrusting stones, shells, and larger stems; taken at 

 five shore stations and thirty-one dredging stations. Green- 

 land to Nova Zembla and southward on the American coast to 

 Nantucket and No-mans-land Islands. 



The white zoarium forms rough encrustations, or extends 

 shelf -like or in frills from the sides of stems. Younger zooecia 

 have a row of areolae around the margin, with strong ribs 

 running often to the base of the rostrum. In older zooecia the 

 secondary calcification becomes very heavy, covering the ribs, 

 the raised margins, and even the rostrum and ooecium, pro- 

 ducing a rather smooth flat layer. The primary aperture is 

 round, with a straight proximal border; the secondary aper- 

 ture is pyriform, the smaller end enclosing the rounded sub- 

 oral avicularium. The ooecium is subglobose, smooth, im- 

 perforate, and prominent in the young state, but later im- 

 mersed in the continuous crust. 



Porella skenei (Ellis and Solander), 1786. PL 12, figs. 

 7-8. (Whiteaves, 1901, p. 104, synonymy, references. Gulf of 

 St. Lawrence and Le Have Bank, Nova Scotia ; Osburn, 1912 a, 

 p. 285, references. Cape Sable, Nova Scotia.) Rare, taken 

 only once, near Egg Rock, encrusting a stone. Kara Sea to 

 Greenland and south along both coasts, in Europe to south- 

 western France, on the American shore to St. Georges Bank, 

 in the Gulf of Maine. 



