22 M. FOSLIE. [1899 



This species appears to be much varying both in habit and 

 with regard to structure. The material at n:iy disposal is too scarce 

 to draw any defined limit of the species, as it seems to vary 

 according to local conditions as well as the substratum. The form 

 considered to be the typical one, or at least that which underlies 

 Dufour's description, in a young state on the one side rather 

 reminds one of Lithothamnion Lenormancli in habit and, on the 

 other hand, Dermatolithon hapalidioides, in general appearance 

 especially approaching certain forms of the latter after the upper 

 part of the conceptacles has fallen away. As regards structure 

 the said variation is especially due to the hypothallus as well as 

 the cells considered to be heterocysts (cp. Solms, Corall. Monogr. 

 t. 1, fig. 2). The latter partly are numerous partly rather scarce 

 even in one and the same specimen, and much varying also with 

 reference to the size. ln one of Dufour's specimen I have seen 

 them even in the lovver part or towards the base of the roof of 

 a conceptacle. 



The form proiyinqiia differs from f. genuina b}^ the new 

 formations over the primary crust fully or almost fuUy anastomo- 

 sing, so that it sometimes even looks as if a ticker crusc consists 

 of a continuous layer of cells, but really being composed of new 

 formations over each other, only more closely united than in the 

 most extreme forms of f. genuina. Therefore, the structure in 

 this form is also somewhat differing, but this is especially due to 

 the hypothallic cells, while the perithallic cells agree with those in 

 f. genuina, being, however, generally a little smaller. In the latter 

 the perithallic cells vary between 12 and 25, now and then up to 

 30 fj. long, and in f. propinqua 10—20 y-, and commonty with 

 thicker walls, but of the same breadth in both. The heterocysts 

 are more scarse and frequently a little smaller in the last mentioned 

 form. Now and then we find m both forms solitary cells in the 

 perithallic layer which are perceptibly larger than the adjacent cells. 



The species appears to be^widely dispersed in the Medittera- 

 nean. I have seen specimens from the Italian coast (Dufour), the 

 Mediterranean coast of France, Antibes (Bornet), and the African 

 coast, near Alger (Debray). 



