15 



n-0 ruffl 



A 



Fig. 6. Lithothamnion Rosmbergi K. Mart. 

 JX 50; B X 23; CX 32. (After Martin). 



the description 1. c, I think the fig. 6 A (the fig. 6 of the original) is to be lookecl upon as 



the proper type of the species. But of this one I have only seen the picture. To judge from 



the picture, the supposed sporangia are of 



another form than usually found with Archaeo- 



lithothamnion, but this may be owing to an 



accidental obliquity of the section. They are, 



however, according to the picture surrounded 



with a structureless m a s s , which seems 



to show that this part of the figure cloesn't 



represent any calcareous alga, whereas the 



parts situated above and below are likely to 



be such ones. According to Martin 1. c. the 



cells here are 10 u. long and broad. In 



sections of fossil sediments with calcareous 



algae, as well as of recent forms of the latter, 



we will frequently observe that layers of 



crustlike calcareous algae occur alternating, occasionally even quite regularly, with certain 



species of lower animals. It is not improbable that fig. 6 A represents such a state of things. 



As a matter of course I don't venture to express any decided opinion, judging from the picture 



alone, and I therefore still subsume the species under Archaeolithotliamuioii. 



The form reproduced in fig. 6 B is found in section "123 Soëk v. Rosenberg (8)". It 

 is "von dem Eilande Soëk im Geelvink Busen, an der Nordküste von Neu-Guinea". — 

 "Unter den Organismen herrscht Lithothamnium hier so sehr vor, dass es geradezu gestein- 

 bildend auftritt und man in Dünnschliffen ausser dieser Pflanze oft nur noch sparliche, die 

 Zwischenraume ausfüllende Kalkspathkörnchen wahrnimmt" J ). This form is no doubt to be referred 

 to the group of calcareous algae which form thin crusts or foliaceous thallus like LitJiotlicuunion 

 lichenoides, L. fragilissimum and other species. The thickness of the crust in the section is 

 330 — 450 tj.. The central cells of the coaxial hypothallium are 22 — 32 p. long and 8 — 11, 

 seldom up to 14 u.. broad, with rather thin walls. The cells of the perithallium are commonly 

 squarish, 6 — 10 p. in diameter, with the greater length partly in horizontal, partly in vertical 

 clirection. In the former case they may be only 5 p. by 9 p., in the latter case very seldom 

 up to 14 p. long. This form being compared with L. fragilissimum, the perithallic layers of 

 both species will show almost complete conformity. The structure of the hypothallium is also 

 much the same as in L. fragilissimum, but the cells are here mostly longer. I have previously 

 pointed out that the hypothallium can be much varying with several calcareous algae and show 

 a comparatively greater variety than the perithallium, a fact which is — partly at all events - 

 owing to the shape and nature of the substratum. In the case in hand the variety is even less 

 than in several recent species. The material, however, is scarce, and the fossil form is sterile. 

 Therefore, I don't venture to identify it at present, but at any rate I must consider it as a 



1) K. Martin. Lithothamnium in cretaceUchen und jüngeren Ablagerungen tropischer Insein. — Centialbl. für Mineralogie 

 etc. 1901, p. 163. 



