HYDROIDS FROM NOVA SCOTIA 167 



Genus Obelia. 

 Obelia commissuralis McCrady. 



Obelia commissuralis McCrady, Gymno. Charleston har., 

 1858, p. 95. 



Obelia commissuralis Nutting, Hydroids of Woods Hole, 1901, 

 p. 350. 



Obelia commissuralis Whiteaves, Marine Invert. Eastern Can., 

 1901, p. 23. 



The commonest campanularian of the region; on rocks, piles, 

 seaweeds, etc., at or below low water, Canso. 



Obelia dichotoma (Linnaeus). 



Sertularia dichotoma Linnaeus, Systema Naturae, 1758, p. 812. 



Obelia dichotoma Nutting, Hydroids of Woods Hole, 1901, p. 

 350. 



Obelia dichotoma Whiteaves, Marine Invert. Eastern Can., 

 1901, p. 23. 



Common on Laminaria, at and below water, Canso. 



Obelia geniculata (Linnaeus). 

 Plate XII, figs. 1 and 2. 



Sertularia geniculata Linnaeus, Systema Naturae, 1767, p. 1312. 



Obelia geniculata Nutting, Hydroids of Woods Hole, 1901, p. 

 350. 



Obelia geniculata Whiteaves, Marine Invert. Eastern Can., 

 1901, p. 23. 



In 3 fathoms, Barrington Passage; on laminaria and other 

 seaweeds, on piles, etc., at low water, Canso. 



Some abnormal specimens of this species were found growing 

 on Lemargus margilis — a copepod, parasitic on a sunfish (Mola 

 mola), caught in Chedabucto bay. In normal specimens, the 

 hydrothecae appear in regular alternation to give the regular 

 geniculate appearance of the stem. The gonophores appear in 

 the axils, being regularly disposed but not in any way affecting 

 the geniculation of the stem. In this case the gonophores take 

 the place of the hydrothecae, making up a portion of the regular 

 geniculate arrangement, and do not appear in the axils. 



24853—11 



