1902,] NATURAL SCIENCES OF PHILADELPHIA. 277 



Spirorbis verruca (Fabr.) Morch. 



Found only with the last, than which it is less conunoii, attached 

 to the tubes of Northia. Specimens measuring 7 to 8 mm. across 

 the spiral were found. 



Spirorbis spirillum (Linn.) Miuch. 



In addition to the typical open spiral form there have been re- 

 ferred to this species numerous examples which, while having, so 

 far as could be determined, identical characters of sette, operculum, 

 etc., have the tube usually coiled in a flat spiral of smaller size 

 and less pellucid character. This form occurs abundantly in com- 

 paratively shallow waters, attached in the manner of Spirorbis 

 borealis, from which the tube is distinguished at once by the reverse 

 direction of its coil, to Laminaria and other resistant thalloid alga?. 

 "When attached to a clean surface of the alga the plane of the spiral 

 is always perfectly flat ; when, however, as frequently occurs, the 

 annelid is associated with an incrusting growth of bryozoaus, the 

 coil of the former immediately becomes elevated and open, approach- 

 ing the typical form which is found in deeper waters associated 

 with hydroids and branching bryozoans. As noted by Michaelsen, 

 this species reaches a much larger size than has been recorded by 

 Levinsen and other students of Arctic Pol ych seta. One of the 

 largest examples, occurring in the collections from Olridir Bay, 

 measures 8.5 mm. in height of the spiral. The typical form is 

 represented from the following localities : South of Cape Alexan- 

 der, O. 26, 27 fath. ; Olridir Bay, O. 49, 15-20 fath. ; Karnah, 

 O. 50, 30-40 fath. ; Robertson Bay, O. 51, 35-40 fath. The flat 

 form occurs as follows: Upernavik, C). 4, 5-10 fath.; Saunders 

 Island, O. 9, 5-10 fath.; Northumberland Island, O. 11, 10-15 

 fath. ; Robertson Bay, O. 51, 5-15 fath. ; Foulke Fjord, (). 54, 

 5 fath. 



Spirorbis vitreus (Fabr.) Morch. 



A single example attached to the tube of a Northia conchylega 

 from Foulke Fjord, O. 39, 14 fath. 



