126 L. HILLIS-COLINVAUX 



entangled but at most adhering only slightly; filament walls thickened and 

 pigmented at the node, and in the cushion joint and stalk region. 



Lectotype specimen. Collected by Krauss at Durban (Natal Bay), 

 South Africa (BM). 



Habitat. Growing on rocks near low-water mark and under 

 ledges of reef pools, also dredged to — 40 m. 



Geographical distribution. Subtropical; western Indian Ocean, 

 both north and south; south-eastern Indian Ocean; south-western 

 Pacific. 



This range includes the first authentic material I have seen from 

 the northern hemisphere. It was collected by R. Norris at Okah, 

 Gujarat State, India, 9 March, 1963 (Smithsonian Oceanographic 

 Sorting Center No. 28). 



This species differs from all other species of the genus in the presence 

 of what have been called "stalked" as opposed to "sessile" segments at 

 the base of a few segments of the thallus. The "stalk" consists of either 

 a small cushion segment or a stalk region or both. 



The medullary filaments, subsequent to fusion in twos and threes in 

 the node region of a typical segment, may extend into a "cushion" 

 segment which consists of cortical layers as in a regular segment. 

 However, the inner layers are usually not as regular in appearance or as 

 extensively developed. In cushion segments near the base of the plant 

 the cortex may be replaced by rhizoidal filaments. Such segments are 

 readily recognized by their looser, rather disorganized appearance. The 

 walls of the main filaments in cushion segments and often those of their 

 branches are somewhat indurated. This is evident in section, and also 

 in surface view of the peripheral utricles, although care must be taken 

 in the latter to distinguish between actual thickening and the effects 

 of shrinkage. 



At the apex of these cushion segments, the medullary filaments 

 commonly branch dichotomously, but may also remain unforked. 

 Either way they usually become torulose and proceed uncorticated for 

 some distance. This represents the stalk. These filaments ultimately 

 branch, generally trichotomously, and their rami develop the cortical 

 layers of the new segment. 



The preceding account describes the complete expression of the 

 "stalk" region between segments. The extent of its development varies 

 with the individual specimen, and it may be influenced by age since it 

 was rather uncommon in the few young plants observed. Rarely does a 

 plant occur without either of these structures being interposed between 

 some of its segments. 



