92 L. HILLIS-COLINVAUX 



5. Node consisting of a single medullary filament; plant growing at 



approximately — 25 m and deeper . . . . . . H. cryptica, p. 154 



5. Node consisting of several to many medullary filaments . . . . 6 



6. Growth pattern often forming laterally spreading thalli to 0-25 m 

 or more which may be accompanied by some erect growth, or 

 growth pattern mostly erect producing densely branched clumps ; 

 branching often multidirectional so that thallus does not lie flat; 

 holdfast attachment generally in several places rather than by a 

 single basal holdfast attachment although these may be lost in 



the collecting . . . . . . . . . . . . . . . . 7 



6. Other than the above. . . . . . . . . . . . . . 8 



7. Branching commonly in one plane so that thallus lies relatively 

 flat; segments generally flat but sometimes arched, commonly 

 white, glossy, broadly subcuneate, sometimes trilobed; cortex 

 generally of two layers of utricles with secondary utricles slightly 

 to distinctly clavate at apical end ; secondary utricles supporting 



four to eight peripheral utricles . . . . . . H. gracilis, p. 144 



7. Branching commonly multidirectional so that thallus does not lie 

 flat; segments flat or contorted, their surfaces dull; cortex 

 generally of three or more series of utricles which are not expanded 

 at the apical end and which bear only four peripheral utricles at 

 most; the commonest species of many rocky areas in extremely 

 shallow water ( — 0-3 m) where it grows as sprawling skeins, or as 

 densely branched clumps . . . . . . . . H. opuntia, p. 110 



8. Mature plants small, not exceeding 5 cm in length ; the segments of 

 at least the upper half of the plant spherical or tear- shaped, to 

 5 mm long, 5 mm broad and 5 mm thickness ; secondary utricles 

 capitate (Fig. 20, No. 12), supporting 6-18 peripheral utricles . . 



H. lacrimosa, p. 147 



8. Mature plants larger ; segments flat or somewhat contorted, but not 

 spherical . . . . . . . . . . . . . . . . 9 



9. Peripheral utricles each projecting into a central spine; surface 

 of clean plants somewhat rough to the touch, colour on drying 

 often bluish-green . . . . . . . . . . H. scabra, p. 127 



9. Peripheral utricles with smooth surface, a central spine being 



absent . . . . . . . . . . . . . . . . . . 10 



10. Secondary utricles noticeable inflated, generally exceeding 90 (xm 



in diameter (Fig. 20, No. 11) . . . . H. discoidea, p. 136 



10. Secondary utricles less than 90 [ini in diameter . . . . . . 11 



11. Diameters of secondary and tertiary utricles swollen in comparison 

 to diameters of the medullary fllaments, and utricles noticeably 

 contracted at their bases . . . . . . . . H. tuna, p. 122 



11. Diameters of secondary and tertiary utricles not appreciably 

 greater than diameters of medullary fllaments, secondary and 

 tertiary utricles not conspicuously contracted at their bases . . 12 



