THE MOUNT DESERT REGION 345 



PoRELLA Gray, 1848 



PoRELLA PROPiNQUA (Smitt), 1867. PL 12, figs. 3-4. (Os- 

 burn, 1912, p. 248, synonymy and references ; 1912 a, p. 285, 

 Cape Sable, Nova Scotia ; Whiteaves, 1901, p. 105, Gulf of St. 

 Lawrence.) Very common on stones, shells, and stems, on 

 hard bottom ; dredged at forty-two stations and taken at one 

 shore station. A common northern species, Spitzbergen, 

 Greenland, and south to the waters about Cape Cod. It does 

 not extend so far south on the European coast, being recorded 

 only from northern Norway. 



Zooecia large, convex, surface roughened by raised ribs 

 which extend part way toward the center from between the 

 marginal pores. A raised border separates the zooecia. The 

 rather large aperture is rounded distally, somewhat narrowed 

 proximally by a pair of lateral denticles. Peristome only 

 slightly raised in infertile zooecia, but when ooecia are present 

 the peristome is carried up on the sides of the aperture into 

 a pair of flap-like projections which are continued forward 

 upon the ovicell and backward to partially or entirely enclose 

 the oral avicularium. Immediately behind the aperture is a 

 rather large avicularian chamber, bearing a round avicula- 

 rium. A large broadly spatulate avicularium is occasionally 

 present on the front of the zooecium and rarely this type may 

 replace the small round oral one. The large, subglobose 

 ooecium is punctured, the pores often arranged in an outer 

 ring and a central cluster. The dorsal wall of the zooecium 

 is perforated by numerous small punctures. 



PoRELLA AciTTiRosTRis Smitt, 1867. PI. 12, figs. 5-6. (Os- 

 burn, 1912, p. 248, Cape Cod; Whiteaves, 1901, p. 103, Gulf of 

 St. Lawrence.) Not very common, encrusting stones and 

 shells, taken at shore stations 11 and 42 and dredged at sta- 

 tions 94, 118, 121, and 126. A high northern species, distrib- 

 uted from Franz Josef Land to Greenland and south on the 

 American coast to Cape Cod. In Europe it occurs southward 

 only to northern Norway. 



The zoaria form thin and usually very regularly arranged 

 incrustations on flat surfaces. The zooecia are of moderate 



