72 L. HILLIS-COLINVAUX 



sections of the genus are established using this character. They are 

 RhipsaHs, Opuntia, Hahmeda, Micronesicae and Crypticae. 



The presence of a special starch-storing body (amyloplast), xylan in 

 the filament walls and a life-history that involves the death of the alga 

 after sexual reproduction in the Caulerpa-Halimeda-Udotea group of 

 algae, or at least in the genera examined, is the basis of a recommenda- 

 tion that this groap of algae be placed (or retained, depending on the 

 system of classification) in an order Caulerpales which would be separate 

 from an order Derbesiales containing Codium, Bryopsis, Derbesia and 

 related genera. 



IV. Taxonomy of the Genus Halimeda Lamouroux 

 A. Introduction 



In this section descriptions are provided for 30 species of Halimeda, 

 as well as for the genus. Two keys are given, one to all the species, the 

 other to the Atlantic taxa together with a list of Atlantic species. A list 

 of Indo-Pacific species is provided but not a separate key because over 

 two -thirds of the species are present in that region. 



In choosing key characters I have avoided as much as possible those 

 which involve extensive preparation of material. Microscopic characters 

 can be checked when the identification has been made. This approach 

 precludes the necessity of detailed microscopy for a single species 

 identification. Within the limits of reliability macroscopic characters 

 are the first pair of choices, and at times it has seemed sufficient that 

 such characters provide the sole choice. At other times they are supple- 

 mented with microscopic characters. 



The characters used in the species descriptions and in the keys were 

 described in Section III. Some of the figures and tables presented 

 therein will be useful here as well, particularly Fig. 17, showing peri- 

 pheral utricles in surface view ; Fig. 20, longitudinal sections of cortex ; 

 and Table III, nodal filament patterns. Table X, in this section, 

 presents a sjaiopsis of important taxonomic characters for the species, 

 together with geographic ranges. 



Section III, A.2.b on preparation oi Halimeda for microscopic study 

 should also be useful. 



1. Materials studied 



The specimens examined for the Halimeda revision (Hillis, 1959) 

 provided the nucleus consisting of the 451 "representative specimens" 



