ECOLOGY AND TAXONOMY OF HaUmeda 129 



separate or else adJiere for an average distance of 30 (xm, whereas in the 

 Caribbean H. tuna the filaments are usually attached laterally for an 

 average length of 85 [j,m. 



HaUmeda lacunalis Taylor 

 Figure 38. 



HaUmeda lacunalis Taylor (1950), p. 91, Plate 51; Hillis (1959), p. 349, 

 Plates 1, 5-7, 9. 



Plants erect or somewhat flaccid, arising from a small holdfast region, 

 to 18 cm tall; calcification light to moderate; the surface often glossy; 

 branching complanate, sometimes sparse, commonly dichotomous but with 

 up to four segments arising from a single one ; basal segments often relatively 

 small and subcylindrical to subcuneate; suprabasal segments at times 

 fusing laterally, others occasionally ribbed, most commonly subcuneate or 

 obovate, but also discoidal or reniform, to 15 mm long, 20 mm broad, and 

 averaging 0-50-0-75 mm in thickness. 



Cortex of two to four layers of utricles; outermost utricles sometimes 

 thickened towards the periphery, remaining attached after decalcification for 

 an average distance of 13 ji,m, 20-55(-70) [in\ in surface diameter, 45- 

 100(-190 in subcylindrical segments) [j,m long in section; two, four or 

 occasionally five borne on each secondary utricle; secondary utricles 

 15-50(-60) [j,m broad, (15-)23-80 \xn\ long, these small utricles absent at 

 times; innermost utricles 35-80 [xm broad. 



Nodal medullary filaments fusing completely in twos and threes ; resultant 

 units entangled and adhering strongly for approximately 80-150(-280) [xm. 



Type specimen. Marshall Islands, Enewetak Atoll, Taylor 

 46-464, 6 June, 1946 (MICH). 



One special form has been described. 



f. lacunalis f. lata (W. R. Taylor) Hillis 



HaUmeda lacunalis f. lata (W. R. Taylor) Hillis (1959), p. 349. 

 HaUmeda gracilis f. lata Taylor (1950), p. 83, Plate 42. 



Plants some tunes rather lax, but generally compact; segments usually 

 broader than long, occasionally subcuneate but more generally discoid to 

 reniform, to 15 mm long, 20 mm broad, and averaging 0-75-1 -00 mm in 

 thickness. 



Type specimen. Marshall Islands, Bikini Atoll, Enyu Island, 

 Taylor 46-21, 15 March, 1946 (MICH). 



Habitat. The known depth range for the genus is 1-55 m. At 

 Enewetak, the form f . lata was relatively common in the fast-flowing 



