Howe: Phycological studies 



497 



distributed as Halimcda Lessonii Hory, but we have no conclusive 

 proof that it is an authentic representative of what Bory intended 

 to have bear this name. Moreover, this alleged name of Bory's, 

 so far as the literature of the subject is concerned, appears to be 

 merely a " nomen nudum" without even an indication of the 

 source of the specimen beyond what one may infer from the name 

 itself, and it therefore deserves no recognition in synonymy. 



Halimcda discoidea has of late been confused chiefly with //. 

 Tuna forma platydisca (Decaisne) Barton. The original specimen 

 of H. platydisca Decaisne (in herb. Mus. Paris.), as already de- 

 termined by Mrs. Gepp, seems to be simply a very large condition 

 of Halitncda Tuna. Its peripheral utricles show occasional fusion, 

 but they have the form and light contact of //. Tuna and the 

 utricles of the subcortical layer also are those of H. Tuna and 

 the plants have the heavier calcification of that species. The seg- 

 ments of Halinieda discoidea are usually but not always larger and 

 more inclined to be obovate than those of H. Tuna and by these 

 characters, together with the lighter calcification of H. discoidea, 

 the two species can usually be distinguished at sight, but reliable 

 diagnostic characters can always be found in the amount of contact 

 of the peripheral utricles and in the form and size of the utricles 

 of the subcortical layer. The more important histological char- 

 acters of the two species are contrasted below : 



Calcification. 



Ilalimeda Tuna 

 Moderate. Involving subcor- 

 tical layer, often also the 

 medulla and the bases of 

 the peripheral utricles but 

 rarely extending to the 

 surface. 



H. discoidea 

 Slight. Usually confined to 

 the distal ends of the 

 utricles of the subcortical 

 layer. 



Peripheral titricles. 



Rounded-truncate, 30-70/4 in Truncate, 40-85U in diam- 



diameter, very rarely fused, 

 in contact above with those 

 adjacent for -^-q-\ their 

 length, not interlocked, 

 rather easily separable on 

 decalcification. 



eter, often fused, in contact 

 above with those adjacent 

 for \-\ their length, inter- 

 locked, separable with much 

 difficulty on decalcification. 



O. Beccari, of Florence, in response to our request to see this type, has sent us a frag- 

 ment of a plant collected by himself at Singapore, with the explanation that it is a portion 

 of the specimen examined by Mrs. Gepp. This Singapore plant, which had been labeled 

 Halittieda papyracea Zan., is evidently a form of //. Tuna, as already determined by 

 Mrs. Gepp. 



