Plants small, usually not exceeding io cm., fragile, branched in one plane di-or trichotomously. 



Joints almost semicircular to reniform and ovate-elliptical, flat, unribbed, margin entire, 

 thickened; varying in size to 24 mm. broad, 15 mm. long, 0.5 mm. thick. 



Filaments of central strand fuse in twos or threes at apex of joint, fused filament varying 

 in length, branching later di-or trichotomously. Peripheral cells 1 50 7. to 175;/ across in surface 

 view-, up to 230 u long. Separated from one another by a mass of calcification. 



This species is closely allied to H. Tuna, trom which it is distinguished by the size ot 

 the peripheral cells, which are the largest known in the genus. They are about three times 

 the size of the average peripheral cells in //. Tuna and six or seven times the size of the 

 average of those in H. Opuntia. Their size and form are clearly visible to the naked eye and 

 they give the plant a characteristic pitted appearance not seen in any other species. Their side 

 walls are calcifiecl throughout their length and are widely separated from those of adjacent 

 cells by a thick incrustation ; on decalcification, therefore, the cells drop apart. The stalkdike 

 base of each peripheral cell is very short; and the subcortical layer is markedly insignificant 

 as compared with that of other species, being composed of short filaments, each filament pro- 

 ducing only a few peripheral cells. 



The central filaments above the point of fusion, in most species quite bare of branches, 

 give rise in II. macrophysa to a few scattered branches, bearing at their ends one or two 

 peripheral cells (fig. 16. p.). 



Although size of the peripheral cells forms as a rule an unstable character in this genus, 

 it has till now been found constant in H. macrophysa. The smallest cells seen in this species 

 have not measured less than 150 <j. across, while in H. Tuna, which shews the same mode of 

 fusion of the central filaments, the peripheral cells have not been seen to exceed 75 u. across. 

 We re it not for this difference H. macrophysa could no longer be retained as an independent 

 species, but would be merely a form of H . Titna. The links which ma)" connect the two species 

 as regards this character have however yet to be found ; in the meantime H. macrophysa seems 

 best considered specifically distinct. 



This species is only recorded at present from the Eastern side of the Indian ücean and 

 from the South Pacific. It has not been collected north of the Equator. 



4. Halimcda Opuntia Lam. 



"Sur la Classif. cl. Polyp. corall. etc. - ' in Soc. Phil. N. Buil. Paris III. 1812. p. 186. 

 Corallina latifolia, et Opuntia marina Plukenet, Phytogr. Tab. 26. fig. 1. Almagestum 118, 



London 1696, non Cortusi. 

 Corallina opuntioides, ramulis densioribus, et foliis magis sinuatis atque corrugatis Sloane, Nat. 



Hist. Jam. vol. I. 1707. p. 57. XVI. Tab. 20. fig. 2. 

 Sertularia ramosissima, articulis reniformibus compresso-planis trichotomis Linn. Hort. Clitï. 



1737. p. 480. in part, et Roven, Flor. Lugd. 1740. p. 523. in part. 

 Articulated Coralline of Jamaica Ellis, Essay. Nat. Hist. Corall. 1755. p. 53. pi. XXV. tïgs. B. b. 

 Corallina Opuntia L. Syst. Nat. vol. I. 1760. p. 805. in part. 

 Corallina Opuntia Pallas, Elench. Zoophyt. 1766. p. 420. 



Corallina Opuntia Esper, Pflanzenthiere. Th. II. Corallina. 1798 — 1806. Tab. I. 

 Corallina opuntioides minor Petiver, Pterigraphia. [767. Tab. XX. fig. 19. 

 Corallina Opuntia Ellis et Solander, Nat. Hist. Zooph. 1786. p. 1 10. Tab. 20. fig. b. 



