504 Howe: PHYCOLOGICAL STUDIES 
Halimeda simulans and has some of the other minor peculiarities 
of the true 1. ¢ridens. 
In its nearly sessile plants and in the form of its segments, 
Halimeda simulans sometimes outwardly resembles H. Tuna, but 
its segments are much thicker and more rigid than in that species 
and they commonly have marginal crenulations or sometimes 
short lobes which are wanting in H. Zuna; and the behavior of 
the filaments of the central strand at the nodes is very different in 
the two species. On Culebra Island, Halimeda simulans, fl. 
Luna, and H. tridens were found growing within short distances 
of each other, and no intermediates were discovered. On the out- 
side shore of the outmost of the Bogue Islands, Montego Bay, 
Jamaica, on January 7, 1907, H. simulans was found growing side 
by side with 1. Tuna, while within a few rods were H. tridens and 
Hf, Monile, and no forms showing any intergrading among these 
four species, as we prefer to call them, were observed. From 
Frozen Cay, Berry Islands, Bahamas, the only Halimeda that we 
brought away besides the H. simulans was one of H. scabra, but 
Hlalimeda tridens is in general rather common throughout the 
Bahamian archipelago. 
A key to the American representatives of the Halimeda tridens 
group may be arranged as follows: 
Filaments of the central strand coherent at the nodes, communicating there with those 
adjacent by pits or very short tubular processes, rarely (now and then in H. 
Monile) merely thick-walled at the nodes and separable ; segments flattened oF 
subterete, often 3-lobed or 3-dentate. 
Peripheral utricles less than 80 u in average maximum diameter, surface view. 
Peripheral utricles 49-77 « in average maximum diameter, surface view; S€S” 
ments usually flattened, H. tride: 
Peripheral utricles 30-44 « in average maximum diameter, surface view- 
Segments mostly subterete. H Monile. 
Segments discoid (suggesting H. 7; una). Hi. simulans. 
e 
Peripheral utricles 175-1904 in average maximum diameter, surface view. 
H. fi 
D. On THE SPORANGIA OF AVRAINVILLEA NIGRICANS 
(PLATE 28, FIGURES 8-25) 
On January 5» 1907, at Montego Bay, Jamaica, while washing 
and Preparing some specimens of Avrainvillea nigricans and A. 
longicaulis (A. Mazet) which had been collected there in shallow 
