148 Proceedings of the Royal Physical Society. 



I have received only a minute portion, without vesicles. 

 Bay of San Francisco. 



3. Sertularia corniculata, Murr. Plate VI. fior. 3. 



Cells not quite opposite, sometimes nearly alternate, form- 

 ing an open cup resting on the stem ; lip not distinct ; exterior 

 margin somewhat projecting at tip ; a single one in the axilla 

 of each pinna. Vesicles pear-shaped, with two long points 

 projecting like horns at the thick end ; aperture between them. 



This is a very elegant little species, and is easily distin- 

 guished by the two long horns at the top of the vesicles, which 

 remind one somewhat of a fool's-cap, and by the wholly open 

 cells. 



Bay of San Francisco. 



4. Plumularia gracilis, Murr. Plate VII. fig. 1. 



Stem slightly flexuose, branched; branches alternately pin- 

 nated ; cells ranked closely in twos and threes ; tubulous, with 

 a plain rjm slightly peaked in front ; vesicles oblong-oval. 



The characters of this Plumularia do not differ greatly from 

 those of P. falcata ; but its habit is so different that it can 

 scarcely be mistaken for it. The branches are closer, and 

 more thickly set, than in P. falcata ; their arched disposition 

 is wanting ; and the whole plant has more the aspect of a Ser- 

 tularia than a Plumularia. The cells are proportionally 

 larger than in P. falcata ; instead of a plain truncate rim, 

 it has one slightly peaked in front, or excised at the sides. 

 Each cell has also a sort of support, like a triangular buttress, 

 below it, marked or lined off from the cell itself. 



Bay of San Francisco. 



5. Plumularia struthionides, Murr. Plate VTI. fig. 2. 



Shoots simple, plumous, the pinnae alternate ; cells close, 

 each occupying the whole of one side of the joint to which it 

 is attached, cup-shaped, with a toothed margin, of which the 

 teeth are unequal, the one in front projecting much more than 

 the rest ; vesicles gibbous, girt with toothed ribs. 



This species is nearly allied to P. cristata, but is much 

 closer in habit, both the pinnae and the cells being nearer each 



