We have here an Alga allied on the one hand to Struvea, 

 from which it abundantly differs in the absence of stipes, and 

 in want of symmetry of parts ; and on the other, to Anadyomene, 

 from which the different arrangement of its component cells 

 separates it. A similarity, too, with the oppositely branched 

 Cladophora, some of which have anastomosing ramuli, may be 

 recognized. 



Probably the Sydney specimens would be referred by De- 

 caisne to his M. Velleyanum, but On comparing with specimens 

 from the Mediterranean and the Friendly Islands, I am unable 

 to detect any specific character between them. If I judged 

 from the figure given by Montagne of his Anadyomene Calo- 

 dictyon (M. Calodictyon, Dne.), I should be disposed to include 

 it also as a synonym ; but, not having seen an authentic speci- 

 men, I abstain from reducing that species. It seems, however, 

 improbable that, in a genus consisting of two very closely allied 

 species, one should have so very wide a range as to be found in 

 the Mediterranean, the Indian Ocean and the Pacific, and the 

 other to be confined to a single rock-pool in the Island of 

 Teneriffe. 



Vig. I. Microdictyon Agardhianum, — the natural size. 2. Portion of the 

 network, — magnified. 3. A few cells, from the same, — more highly magnified. 



