494 Howe: PHYCOLOGICAL STUDIES 
from the margins of the segments (PL. 28, FIG. 3) are mutually 
coherent near the point of emergence and communicate with each 
other there by pits or pores like the vegetative filaments of the 
central strand at the nodes, but the sporangiophores from the 
disc-surfaces originate as direct continuations of the peripheral 
utricles or of the utricles of the subcortical layer and are without 
fusions or adhesions of any kind (PL. 28, Fics. 4-7). The sporangia 
are obovoid or pyriform and are 0.20-0.38 mm. broad. The callose 
or mucous plugs which we have described * as forming basal septa 
of a certain sort for the sporangia of Ha/imeda scabra we have not 
observed in Halimeda tridens ; such are, however, of occasional] 
and irregular occurrence in the Porto Rican material of Halimeda 
una. 
B. ON THE AMERICAN SPECIES OF THE HaLIMEDA TUNA GROUP 
At the time of describing the strongly marked species Halimeda 
scabra,} attention was directed to another species which likewise 
had commonly been confused with Halimeda Tuna. Of this 
“smooth plant of the Yuna-cuneata alliance,’ we remarked, “ It 
seems rather violent to identify it either with Halimeda Tuna or 
with /7. cuneata, and it is possible that further acquaintance with 
it will show constant and reliable characters for distinguishing it 
from both.” At that time nearly all of our American material of 
the Zunxa group belonged to this “ species inquirenda” and to /#. 
scabra and the only specimens we had seen from the American 
side of the Atlantic which we could refer to H. Tuna were from 
Bermuda. But since then we have collected what we believe to 
be the true 17. Tuna both in Porto Rico and in Jamaica and have 
seen a specimen of it purporting to come from Key West, Florida, 
so it now seems probable that both it and its ally are of general 
distribution in the West Indian region. And the two “ forms,” 
se far as we have seen them, are always absolutely and abundantly 
distinct and in our opinion are as much entitled to be considered 
specifically different from each other as are Halimeda Tuna and 
i. Opuntia or Halimeda Tuna and H. scabra. It soon became 
evident that this ally of H. Tuna had already been recognized as 
* Bull. Torrey Club 32: 243. 1905. 
tM. A. Howe, Bull, Torrey Club 32 : 241-244. pl. 11,12. 1905. 
