No. 5] NEW OR CRITICAL CALCAREOUS ALGÆ. 5 



aboiit 4 cm. in diameter. Branches short, 2 — 3 mm. in diameter, 

 with rounded ends, in f. Jwteromorpha branches very short vvith 

 rounded-thickened ends. Conceptacles of sporangia subprominent, 

 450 — 600 /J- in diameter. Sporangia 100 by 30 /j-. 



I have seen but one specimen of each form. The form ge- 

 nuina is attached to a fragment of a shell which it at length sur- 

 rounds, forming a crust about 0.5 mm. in thickness, from which 

 issue subdichotomously divided, short branches, in the lower part 

 frequently much anastomosing, upwards more free, subfastigiate, 

 with rounded ends. Tliis form approaches in habit the above 

 mentioned delicate form under L. hrachycladum. 



The form heteromor])Tia rather differs in habit from f. genuina. 

 It agrees with the latter as regards the conceptacles, and in struc- 

 ture it also very nearly accords with this form. On the other 

 hand, it has very much the habit of a small Litliophyllwm race- 

 mus f. crassa. It is like f. genuina attached to a fragment of a 

 shell. The branches are shorter, a little thicker and more fastigiate 

 than in the said form, with rounded-thickened ends, here and there 

 knotty, and forms a roundish ball about 2.5 cm. in diameter. 



The subprominent conceptacles of sporangia are more or less 

 crowded in the upper part of the branches, 450 — 600 jj- in dia- 

 meter seen from above, and flattened in the central parts, here 

 intersected with _ about 30 delicate muciferous canals. They fre- 

 quently at length grow down into the frond. The tetrasporangia 

 are about 100 /j- long by 30 y-. The walls between the sporangia 

 are generally not dissolved. Especially overgrown conceptacles 

 are in that case on a section easity to be confounded with the 

 sporangia beds in Archæolithothamniofi, sometimes forming a uni- 

 form bed even more than 1 mm. in length and of the same height 

 everywhere, not unlikely owing to confluent conceptacles, with 

 nearly cylindrical, densely crowded, emptied sporangia, with inter- 

 vening, more-celled walls, and then much resembling the emptied 

 sori in the said genus. However, this is not to be seen i f a part 

 of the roof of the conceptacle falls away which apparently often 

 takes place. But it shows, on the othei- hand, a very close con- 

 nection between LitJwthamnion and Archæolithothamnion. Un- 



