1-1 



hypothallic cells are 18 28^. long and 7 — 14 ,u- broad, partly with fairly thick walls, partly 

 thin-walled. In the perithallic layer the cells are partly square or somewhat rounded, partly a 

 little vertically or horizontally elongated, frequently 5—8 <i. in diameter, with rather thick 

 walls, here and there however commonly elongated in vertical direction and up to about i2u. 

 long, very seldom more excepl between crowded conceptacles of sporangia, where the cells 

 may be somewhat longer. I Fig. 5 1. 



The reproductive organs hitherto known are sporangia. The conceptacles are mostly 

 densely crowded on different parts of the crust, sometimes partly confluent, and are in old 

 imens finally overgrown. They are not much prominent, with slightly convexed roof, at 

 length somewhat flattened, circular or oblong in circumference, but often not sharply defined, 

 -450 ij., in diameter, when seen from above. The roof is thin and intersected with 30 — 40 

 delicate muciferous canals. The sporangia are four-parted, about 80 u. long und 30 u. broad, 

 with enduring partition walls between the former. The plant bears these organs in the months 

 of June and November, but rather scantily. 



The species comes nearest to Lithothamnion Engelhartii from the south coast of Australia. 

 It is distinguished from the latter in habit particularly by a thallus more spread and more freely 

 growing. Besides it is brittier. The conceptacles are a little larger and less sharply defined, and 

 there is also some difference as to structure. Young or sterile specimens are, on the other 

 hand, hardly distinguishable from Lithothamnion simulans. 



Occurrence: This species seems to have been best developed at the station 8 1 , from 

 which, however, only a few specimens, more or less fragmentary, are in hand. From the station 7 8 

 only a small fragmentary crust has been brought home, together with L. simulans, and from 

 the station 234 there is only one young specimen, accrete with two or three other species, 

 among which a Squamariacea and perhaps a young L. simulans. 



By the kindness of Professor K. Martin I have had the opportunity of examining some 

 sections of fossil sediments from the Geological and Mineralogical Institut' at Leyden, rnainly 

 from Xew Guinea. These sections include a great number of calcareous algae, among which 

 two of the types of Lithothamnion Rosenbergi K. Mart. ! ). This species I classified in Rev. Syst. 

 Surv. ") as Archaeolithothamnion Rosenbergi according to the description given by Rothpletz 

 in Foss. Kalkalg. 3 ). Having afterwards been acquainted with the original description and the 

 pictures of the species, I find it questionable, whether it includes any Archaeolithothamnion at 

 all. At any rate it includes at least two species, one of which may be identical with Lithotham- 

 nion fragilissimum. big. 6 represents a reproduction of the pictures mentioned. Judging from 



1 K. Mv. I Versteinerungsführenden Sedimente Timors. — Sammlungen des geolog. Reichsmuseums in Leiden. I, Heft i 



(1881), p. 12. t. III. lig. 6—7. 



K. Mai iis. Kine ïertiaerformation von Neu-Guinea uad benachbarten Insein. 1. c. Heft 2 fiSSi 1 . p. 70. 



Systematical Survey of the Melobesieae. — Det Kgl. Norske Vidensk. Selsk. Skrifter. 1900, n° 5. 

 Rotiii'Lei Kalkalgen aus den Familien d:r Codiaceen und Corallinaceen. — Zeitschr, d. Oeutschen geolog. 



1 111. Heft 2 (1S91), p. 295. 



