100 L. HELLIS-COLrNVAUX 



Solander (1786). The earlier synonymy is given by Barton who, in 

 addition to considering monile as a form of incrassata, equated with 

 it cylindracea Decaisne and polydactylis J. Agardh. 



Cylindrical segments, which are a characteristic of monile, also 

 occur in other species. The predominance of them in monile, together 

 with the general form of the plants, usually enables this taxon to be 

 identified macroscopically. In doubtful cases, differences in nodal 

 anatomy and in the diameters of the peripheral utricles, the latter 

 averaging 46 [j,m in monile and 73 [xm in incrassata, are diagnostic. The 

 somewhat modified pattern of the nodal filaments in monile was 

 discussed in Section III, 



Halimeda cylindracea Decaisne 

 Figures 4, 5, 104. 



Halimeda cylindracea Decaisne (1842), p. 103 ; Hillis (1959), p. 373, Plates 4-7, 



12. 

 Halimeda polydactylis J. Agardh (1887), p. 89. 



Halimeda incrassata Harvey (1860), p. 125 p.p. including Plate 125. 

 Halimeda incrassata f. monilis Barton (1901), p. 27 p.p. including Plate 4, 



Fig. 40. 



Plants erect, elongate, usually attenuated from base to apex, to 19 cm 

 tall excluding the holdfast which may extend to over 12 cm in length; 

 branching restricted, mainly ditrichotomous ; basal segments cask-shaped, 

 to 7 mm long, 12 mm broad and averaging 3^ mm in thickness, forming a 

 distinct terete or subterete stalk with the lower forkings often becoming 

 consolidated laterally to form a fan-shaped structure in older plants ; branch 

 segments subcuneate with lobed upper margins, others generally plane and 

 predominantly cylindrical, although at times becoming subspherical towards 

 the plant apex, to 7 mm long, 4 mm broad and averaging 1*5 fxm in thickness. 



Cortex of three to five layers of utricles; outermost utricles tending to 

 separate on decalcification, their lateral and peripheral walls sometimes 

 thickened, 17-45(-55) (xm in surface diameter, 24-62 [xm long in section, 

 two or four supported by each secondary utricle; secondary utricles 17-62 fxm 

 broad, 23-80(-100) [xm long; tertiary utricles 30-90 fxm broad. 



Nodal medullary filaments uniting as a single group for a distance of 

 approximately 34-72 jj.m, the adjacent filaments communicating by pores; 

 walls in this region thickened and pigmented. 



Type specimen. Madagascar, Nossi-Be, Perville (PC). 



Habitat. Grows in unconsolidated substrate, but its holdfast, 

 which is sometimes massive, is frequently attached to one or more 

 fragments of buried broken coral or rock; from about — 0-3 m to 



