HOWE: DIMORPHISM IN GALAXAURA 197 
be surmised that Galaxaura oblongata (Ell. & Sol.) Lamour.® has its 
tetrasporic condition in G. comans Kjellm. And just as the line of 
demarkation between Galaxaura oblongata and G. cylindrica seems a 
little uncertain and arbitrary, so also is the line of separation between 
G. comans and G. lapidescens. Where there is so much difference in 
habit as there is between the ‘“ Rhodura’’ forms on the one hand and 
the ‘“Microthoé” and ‘“‘Eugalaxaura’’ forms on the other, there is 
manifestly more need for a cultural demonstration of their correlation 
as alternating generations than there is in the case of the Cameratae- 
Spissae and Brachycladia-Vepreculae groups, where the two 
phases have the same outward appearance. But while experimental 
demonstration or further observations in the field may be desirable 
for a precise correlation of the ‘“‘Rhodura”’ forms, the existing evidence 
that these ‘‘Rhodura”’ forms represent tetrasporic phases of ‘‘ Micro- 
thoé”’ and ‘“ Eugalaxaura’’ forms seems convincing. 
EXPLANATION OF PLATES III AND IV 
PLATE III 
Photograph of a formalin-preserved antheridial specimen of Galaxaura marginata 
(Ell. & Soland.) Lamour., representing Kjellman’s section ‘‘Vepreculae.’’ Speci- 
men from San Juan, Porto Rico (Howe 2304); natural size. 
PLATE IV 
Fic. 1. Photograph of a formalin-preserved tetrasporic specimen of Galaxaura 
marginata (Ell. & Soland.) Lamour., representing the section “ Brachycladia.”’ 
Specimen from San Juan, Porto Rico (Howe 2304); natural size. 
Fic. 2. Photograph of a formalin-preserved specimen representing a form of 
Galaxaura flagelliformis Kjellm. and belonging in Kjellman’s section ‘‘ Rhodura.”’ 
Specimen from Santurce, Porto Rico (Howe 1859a); natural size. 
Fic. 3. Photograph of a formalin-preserved specimen of Galaxaura squalida 
Kjellm. Specimen from Santurce, Porto Rico (Howe 1859b); natural size. 
6 Galaxaura fragilis of Kjellman and of Borgesen; not Dichotomaria fragilis 
Lamarck, the type specimen of which in herb. Mus. Paris. appears to have the 
structure of the ‘‘Spissae’’ group. 
