44 
Howe: PHYCOLOGICAL STUDIES 497 
distributed as Halimeda Lessonii Bory, 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. 
Halimeda discoidea has of late been confused chiefly with /7. 
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 Halimeda Tuna. Its peripheral utricles show occasional fusion, 
but they have the form and light contact of H. Tuna and the 
utricles of the subcortical layer also are those of H. Zuna and 
the plants have the heavier calcification of that species. The seg- 
ments of Halimeda discoidea are usually but not always larger and 
more inclined to be obovate than those of 7. Zuxa 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: 
Halimeda Tuna H. discotdea 
Calcification, Moderate. Involving subcor- Slight. Usually confined to 
tical layer, often also the the distal ends of th 
t 
medulla and the bases of utricles of the subcortical 
the peripheral utricles but layer. 
rarely extending to the 
surface. 
Peripheral utricles, Rounded-truncate, 30-70% in ‘Truncate, 4o-85 in diam- 
diameter, very rarely fused, : 
with those above with those adjacent 
adjacent for 5-% their for 4-3 
length, not interlocked, locked, separable with much 
rather easily separable on difficulty on decalcification. 
decalcification, 
Halimeda papyracea Zan., is evidently a form of 1. Tuna, as already determined by 
. Gepp. 
Mrs 
