No. 5] NEW OR CRITICAL CALCAREOUS ALGÆ. 21 



With reference to structure, the hypothallus is formed of cells 

 which are up to 10 />- long, frequently shorter, and the anticlines 

 sometimes with a slow sometimes with a rather rapid convergence 

 towards matrix, however now and then with an almost imper- 

 ceptible contrast between hj^pothallus and perithallus. The cells 

 of the latter are verj^ small with rather thick walls, frequently 

 3 — 5 !J. in diameter, square or rounded, or 3 by 4 — 5 p-, often 

 with the longest diameter in horizontal direction. 



The plant stands nearest to Lithothamnion Lenormandi, 

 resembling certain forms of this species in habit, but it sometimes 

 also reminds one of L. læve. On the other hand, it in structure 

 and sometimes also in habit approaches Lithophyllum decipiens. 

 The conceptacles are nearly related to those in Lithoth. synanabla- 

 sium. On a cursory examination i: may be confounded with a 

 very j^oung specimens of the latter. 



It is hitherto but known from the west coast of Africa, at 

 St. Thomé, where it seems to be of pretty common occurrence. 

 One of the specimens is labelled „Bahia de Anna Chaves et Praia 

 Lagarto, leg. A, Moller". Herb. Univ, Coimbra, Prof. Henriques, 

 no. 23. 



Goniolithon (Cladolithon^) Notarisii (Duf.) Fosl. mscr. 

 Melobesia Notarisii Duf. Quadr. Melob. p. 37. 



f. genuina.^) 



Melobesia Notarisii Duf. 1. c. ; sec. spee. 



f. propinqua Fosl. mscr. 



The section Cladolithon in Fosl. List of Lith. p. 8 is to be considered as 

 a subgenus and to be given a somewhat other limit than there. Some of 

 the species preliminary referred to it 1. c. are to be referred partly to the 

 subgenus Lepidomorphum partly (one or two species) to LilJiopliyllum. 

 There can scarcely be any doubt that the alga described by Heydrich 

 in Ber. d. deutsch. bot. Ges. Bd. XVII, p. 221, t. XVII, fig. 5 under the 

 name of Lithophyllum Chalonii very nearly represents an old specimen 

 of the type of the present species, such as the latter has been compre- 

 hended by Dufuor, according to young specimens distributed by himself 

 which I have seen, or at most to be considered as a denominated form, 

 f. Chalonii, as the new formations seem to be more free than in the type, 

 and the heierocysts more numerous. 



