124 L. HILLIS-COLINVAUX 



This species, which was first described for the Mediterranean, 

 has subsequently been attributed to most tropical areas. The specimens 

 from these other regions, however, usually differ in one or more respects 

 from the small-segmented Mediterranean plants which represent the 

 type. 



In habit, the typical small-segmented Mediterranean plants seem 

 small and cushion-like, whereas specimens with small segments from 

 the Atlantic and Indian Oceans are often larger and less compact. The 

 lower segments of western Atlantic plants are commonly subcuneate 

 in shape rather than reniform, and the surface diameters of peripheral 

 utricles in western Atlantic and Indian Ocean material average 

 approximately 50 [xm as opposed to 65 yun for the Mediterranean 

 plants. The tuna plants of Bermuda, a region at the extreme edge of 

 the tropical range, resemble the Mediterranean tuna more closely than 

 do Caribbean plants (Howe, 1905a), an observation well substantiated 

 by herbarium specimens. Some of the observed differences may be a 

 response to a stress environment as well as to geographical isolation. 

 The range encountered in the various characters has been considered 

 within the range of the species. 



Large-segmented plants occur throughout the entire range of tuna 

 and are sometimes assigned to f. platydisca. The surface diameters of 

 their peripheral utricles are at the larger end of the range given. 



Halimeda cuneata Hering 

 Figures 36, 61. 



Halimeda cuneata Hering in Krauss (1846), p. 214; Barton (1901), p. 15, 

 Plate 1, Fig. 7, but not Plate 2, Fig. 9, or Plate 1, Fig. 10; Hillis (1959), 

 p. 345, Plates 1, 5-7, 9. 



Halimeda obovata Kiitzing (1858), p. 11, Plate 25, Fig. 1. 



Halimeda versatilis J. Agardh (1887), p. 86. 



Plants rather loosely organized or occasionally compact, arising from a 

 small but distinct holdfast region, to 25 cm tall ; calcification light ; the 

 surface smooth and usually somewhat glossy ; branching mainly dichotomous 

 but with up to six segments arising from a single one ; the basal first to second 

 segments cylindrical to subcylindrical, often giving the appearance of a 

 short stipe; other segments plane, mostly cuneate, sometimes discoid, 

 generally to 16 mm long, 18 mm broad and averaging 0-50-0-75 mm in 

 thickness, but in some specimens reaching 21 mm in length and 27 mm in 

 breadth; many of the segments supported by a cushion segment, to 1-5 mm 

 long, 5-5 mm broad, or a stalk region of uncorticated medullary filaments, 

 or both. 



