47 



In specimens typically developed the plant forms a rather even crust on divers hard 

 objects, sometimes one crust formed above the other (PI. IX, fig. 2, 3, 5). The crust attains 

 a thickness of up to about 1 cm., frequently however less. It seldom develops excrescences, 

 as far as I have seen. Such ones apparently often occur, but they are, in the specimens 

 examined by me, at any rate as a rule, caused 

 partly by the shape of the substratum, partly 

 by covering up extraneous objects. Besides, 

 they are often due to numerous, finer or wider, 

 passages made by worms, around the orifices 

 of which new formations of tissue are by and 

 by heaped up, or the destruction of the inner 

 layers, especially those just below the surface 

 of the plant, induce local formations of tissue 

 in the shape of more or less wart-like excres- 

 cences (PI. IX, fig. 4). 



A vertical section of the crust exhibits 

 a rather varying structure, with a vigorous 

 and marked coaxial hypothallium. The peri- 

 thallic cells are partly squarish, often however 

 with rounded corners, partly vertically elonga- 

 ted and much varying in size, frequently being 

 largest in specimens which are much attackecl 

 by animals and attached to an uneven sub- 

 stratum (Fig. 1 9 B). The cells are most fre- 

 quently thick-walled. New hypothallic formations 

 are often to be seen, particularly developed over | 

 damaged parts of the plant. Heterocysts appear 

 in great number, and the}- form frequently at 

 length grown-in rows. These rows are inter- 

 preted by Heydrich as "Zeilen der Leitungs- 

 schicht". Cp. 1. c. p. 59, fig. 1. Similar but 

 much shorter grown-in rows of heterocysts 

 also appear in Goniolithon frutescens, although 

 there are frequently to be seen but solitary 

 cells, which in certain specimens are numerous 

 almost in any part of the perithallic layer. In 

 G. Notarisii grown-in heterocysts seldom appear. Cp. Solms-Laubach. Corall. Monogr. t. 1, fig. 2. 



The cystocarpic conceptacles in this species are scattered almost all over the crust. They 

 appear frequently in a rather great number, but they are, on the other hand, never densely 

 crowded. The conceptacles are subconical, rather low and 800 — 11 00 u.. in diameter, when 

 seen from the surface, sometimes, however, even up to about 1,5 mm., but often not sharply 



Fig. 19. Goniolithon Fosliei (Ileydr.) Fosl. 

 A. Vertical section of the specimen pictured pi. IX, fig. i ; 

 />'. Vertical section of the specimen pictured pi. IX, fig. 2, 

 with a new hypothallium formed over a conceptacle; X 72. 



