sides of the midrib and nerves. These only differ from those of a Dasya 

 by the anastomosis of their lower divisions ; the extremities are free, and 

 stand out from the surface like hairs. The general form of the frond resem- 

 bles that of an oak-leaf, between lyrate and pinnatifid ; the margin is fringed 

 with teeth-like, multifid fimbrils, which disappear in old specimens. In the 

 winter season the stems become partially or wholly denuded, and are then 

 found bearing fruit of both kinds. The ceramidia always spring from the 

 midribs and generally near the summits, one on each lobe ; they are shaped 

 something like an amphora, with a long, projecting neck. The stichidia 

 are formed only on the lateral nerves, likewise toward the apices of the lobes ; 

 and what may be called the tetrasporic inflorescence, constitutes an ovate, 

 distichously pinnated, compound spike ; each individual stichidium being 

 very minute, roundish, and producing three or four tetraspores. The sub- 

 stance of the frond, though flaccid and tender, is not gelatinous, and does 

 not soon decay in fresh-water. The colour is rosy, but not brilliant, and is 

 sometimes brownish-red, or tinted with rosy-purple toward the extremities. 

 In drying the plant adheres closely to paper. 



There are some Algae of such elaborate structure, that my 

 rude pencil cannot do them even moderate justice ; and this is 

 one of them. And there are some men so deserving of the 

 honours of science, that no compliments paid to them can add 

 lustre to their name ; and M. Thuret, after whom the present 

 Alga has been named, is such a one. I need not remind algo- 

 logists that it is to his admirable researches, carried on for 

 several years, that we owe a knowledge of some of the most 

 remarkable facts attending the development of Algse and ferti- 

 lization of their spores. 



A second species of Thuretia will be figured in a future 

 number. 



Tig. 1. Thuketia quercifolia, a summer frond. 2. A fragment of the win- 

 ter frond, bearing tetraspores: — both of the natural size. 3. Apex of an 

 old network, with stichidia on the lateral nerves. 4. A small portion of a 

 nerve, with its stichidia, denuded. 5. A tetraspore. 6. A ceramidiuin. 

 7. Spores from the same. 8. Fragment of the net : — all the latter figures 

 more or less magnified. 



