io5 



only one species Litharthron australis Sonder, which has the same diagnosis as the genus. 

 Harvey in his Account of the Marine Botany of the Colony of Western Australia mentions 

 under N°. 155 an Amphiroa sp. . . . , growing with A. australis, to which it is allied. This 

 specimen had however become broken in travelling. It would be interesting to know, whether 

 this plant of Harvey is indeed another representative of the genus Litharthron. 



Arthrocardia (Dec.) Aresch. 



Though there were no specimens of the genus Arthrocardia in the collection of the 

 Siboga, I should like to say a few words about this genus as my researches on the Amphiroae 

 of the Siboga led me to sink many species into the genus Arthrocardia that had hitherto 

 been considered as belonging to the genus Amphiroa. 



The genus Arthrocardia has been sunk by Schmitz and Hauptfleisch into the genus 

 Cheilosporum. However not only these two genera but the four genera Arthrocardia, Cheilo- 

 sporum, Corallina and Jania are closely allied together, much closer indeed, than either of 

 them to the genus Amphiroa. They are probably a separate branch of the family of the 

 Corallineae, just like Ai/iphiroa and Metagoniolithon, but I have not been able to tracé the 

 common ancestor of these four first-named genera. 



Their anatomical structure is almost the same ; in Jania alone the cells have nearly the same 

 length in the joint and in the node, which they do not have in the other genera. But there are 

 species of Jania which have longer cells in the node and seem to bridge over the difference. 

 The position of the conceptacula however marks a difference between the genera: in Arthro- 

 cardia we find conceptacula on the joints as in Amphiroa ; in Cheilosporum we find them 

 immersed in the margin of the broadened, winglike joint, in Corallina and Jania immersed in 

 the frond at the top of the joints. 



We see three stages, each marking a gradation of higher development and I think 

 that the different names may be kept to mark the different stages. Whether they must be 

 considered as names of genera or only of subgenera will depend upon the value one attaches 

 to a character depending upon the position of the conceptaculum and upon the conception 

 one has of a genus. 



To Arthrocardia belong the following species considered by late authors on the subject 

 to belong to the genus Amphiroa : 



1. Arthrocardia cretacea (P. et R.). 



Corallina cretacea P. et R. 

 Amphiroa cretacea (P. et R.) Aresch. 



2. Arthrocardia tubercnlosa (P. et R.). 



Corallina tuberculosa P. et R. 



Amphiroa tuberculosa (P. et R.) Setchell and Gardner. 



3. Arthrocardia cpiphlegnoides (Ag.). 



Amphiroa cpiphlegnoides Ag. 

 Amphiroa rudis Harvey. 



SIBOGA-EXPEDITIE LXI. 14 



