LITHOTHAMNIA. 465 



structure with somewhat stunted growths from the Mediterranean and the Adriatic. The only 

 difference appears to be, that the conceptacles of cystocarps are more acute than generally 

 seen in specimens from the last-named regions. Therefore, there seems to be no reason to 

 consider the alga from the Indian Ocean, hitherto only known from the Gulf of Siam and 

 the Maldives, as a form so differing from the Mediterranean and Adriatic f. clavulata, that 

 it ought to be specially denominated. 



As remarked in a pamphlet in press' there is a considerable difference in habit between 

 a delicate f. clavulata and a coarse f crassiuscula, but I have been unable to draw any 

 true limit between them. They are both pictured in the said pamphlet together with a still 

 more delicate and rather curious form, which I have named f. soluta. A coarse specimen of 

 f. crassiuscula is also to be found in the collection from the Maldives (Plate XXIV. fig. 2). 

 It seems as if this form has a tendency to get a little coarser in the tropics than is generally 

 the case in the Mediterranean or the Adi'iatic, as in the latter regions the greatest number 

 of specimens show slightly thinner branches, although not seldom fully agreeing even in 

 this respect. On the other hand the specimen from the Maldives fully coincides with the 

 same form of the species known from the south coast of Australia, where it seems to be 

 rather abundant. This form probably occurs also in other parts of the Indian as well as 

 Pacific Ocean. 



Besides the specimen of f. crassiuscula four other specimens were found in the present 

 collection. These represent a form which is closely connected with f crassiuscula, but differing 

 in some respects (Plate XXIV. fig. 3). The specimen here pictured reminds one in habit 

 of an old Goniolithon Brassica-flanda, but, as mentioned in the above quoted pamphlet, in 

 the Adriatic as well as in the Mediterranean these two species sometimes rather approach 

 each other in that respect, though otherwise being quite different. These four Maldive 

 specimens form nodules up to about 6 cm. in diameter, which look as if they had been 

 freely developed at the bottom. They suiTound. at least in part, pieces of corals. Their 

 consistency is more compact than in typical f crassiuscula, the surface even a little shining, 

 but, above all, their conceptacles of sporangia are somewhat smaller. The latter sometimes 

 are about 600 fi in diameter seen from above, but in most cases only 400 — 500 fi. They are 

 now and then slightly depressed in the central part, especially towards maturity, and their 

 muciferous canals are somewhat crowded in the roof, as also occasionally occurs in typical 

 specimens of the form. 



In structure this Maldive form coincides in the main with typical L. fruticulosuni. 

 A section shows that the plant has been much attacked by lower animals, and numerous 

 new formations have been built up over each other, in part almost alternating especially with 

 Polyzoa. A consequence of this often seems to be, that the hypothallic layer gets more 

 vigorously developed, or the cells larger and, especially, more elongated than would otherwise 

 be the case. I have formerly shown that, for instance in Lithothamnion Philippii, the corre- 

 sponding cells under similar conditions sometimes become even much larger than under a normal 

 development. This seems especially to be the case when the plant sticks to certain Polyzoa, 

 chiefly coarse and large-celled ones, while on the other hand certain corals seem to give rise 

 to a rather feeble development of the basal layer of the plant. In several of the new 

 formations in the specimens the h}^othallic layer is vigorously developed, more or less 

 coaxillate, and often composed of larger cells than generally observed in the species. The 



1 "Die Lithothamnien des Adriatischen Meeres und Marokkos." Wissemch. Meeresuntersuchungen, Abt. Helgoland. 



