MENIPEA TERNATA. 39 



gated, much attenuated downwards ; aperture oval, 

 occupying a small proportion of the length of the cell, 

 with three spines, two at the top and one some way 

 below it on the outer margin ; operculum small, entire, 

 variable in shape. Lateral avicularia large and pro- 

 minent, generally present on the two lower cells in the 

 internode ; one anterior avicularium on each cell, imme- 

 diately below the aperture, or, very commonly, on the 

 uppermost cell alone, minute, raised; mandible directed 

 downwards. Ooecia elongated, smooth. 



Radical fibres simple, given off from the lower parts of 

 the shoots ; many of the branches furnished with long 

 tendril-like claspers, originating from the side of a cell 

 immediately above the lateral avicularium, near the top 

 of the internode, enlarged and curled above and open 

 at the free extremity. 



Primary cell short, cup-shaped, with a round terminal 

 aperture surrounded by 10 or 11 spines. 



Range op Variation. The cells ai-e sometimes much 

 more elongated than at others, or, I should rather say, 

 the two lower cells in the internode, for the uppermost, 

 which is placed at the bifurcation, is always shorter than 

 the rest, and does not appear to change much. The elon- 

 gation of the cells of course gives a more slender and 

 graceful habit to the shoots. The specific character 

 given above is founded on what seems to be the usual 

 normal form. Occasionally an internode occurs con- 

 sisting of 4-7 cells, the rest being the usual triplets ; but 

 such cases seem to be very rare. The variety gracilis, * 

 described by Smitt from the Arctic seas, has universally 

 a large number of cells in each internode ; the cells are 

 shorter, straighter, and of more equal width throughout 

 than in the present form ; the lateral avicularia are very 

 small, and both the spines and opercula seem to be 

 sparingly developed. I believe that this form, of which I 



