138 L. HILLIS-COLINVAUX 



42 [xm, often fusing laterally in twos, threes and occasionally fours for this 

 same distance, unfused peripheral utricles (30-)40-90 [xm in surface diameter, 

 45-120(-210) (Jim long in section, up to 14 being supported by each secondary 

 utricle; innermost utricles somewhat contiguous at their apical end, or when 

 well developed for most of their length, (70-)95-155(-260) [im broad, 

 100-350(-435) [xm long. 



Nodal medullary filaments united in twos and threes, the fusion both 

 complete and incomplete; fused units entangled but at most adhering 

 only slightly. 



Type specimen. In the Musee National d'Histoire Naturelle, 

 Paris ; label indicates the plant was collected at Kamtschatka during 

 voyage of the Venus ; at least locality incorrect. 



Habitat. Growing erect; associated with rock surfaces which 

 sometimes may be veneered or partly buried with sand; from 

 slightly below low-tide line to — 50 m. 



Geographic distribution. Pantropical; western and eastern 

 Indian Ocean including Red Sea; western Pacific both north and 

 south; north-eastern Pacific, western Atlantic, both north and 

 south; north-eastern Atlantic. 



The epithet discoidea was first applied by Esper (1798-1806, Plate 

 11) to a drawing of Halimeda labelled Corallina discoidea. This plant, 

 apparently Mediterranean, was later placed in synonymy under tuna 

 by Hammer (1830) in his continuation of Esper's work. Even were this 

 relationship not accepted, Esper does not qualify as author of discoidea, 

 since a plate unaccompanied by analysis of parts does not constitute 

 valid publication (Lanjouw et al., 1966). The species discoidea was later 

 described by Decaisne (1842). 



This species, although frequently mistaken for tuna and cuneata, is 

 microscopically distinct, and is characterized in particular by the 

 swollen utricles of the inner cortex, one layer being the most common. 

 When an additional zone is present, it rarely occurs uniformly through- 

 out the segment, the innermost utricles then tending towards the lower 

 limit of the size range. Relatively small secondary utricles often occur 

 in Pacific-Mexican plants, and in some of the Hawaiian discoidea. This 

 irregularity was also noted by Howe (1911). 



Subsequent to the removal, by Howe (1907), of this species from 

 synonymy under tuna where it had been relegated by Barton (1901), 

 three subspecific taxa have been described: v. platyloba (Borgesen, 

 1911) from deep water, f. subdigitata (Gilbert, 1947) including plants 

 which resemble cuneata, and f. intermedia (Gilbert, 1947) contaming 



