15 114 Proceedings of the Royal Irish Academy. 



Description. — Plants rather slender, much branched, 9-15 inches high as 

 a pool plant, 2-2§ feet when growing in deep water. Colour dark green. 

 Fronds slender, 3-4 mm. thick, cyclindrical, often slightly flattened at the 

 axils, dichotomous ; surface often very tomentose, becoming smooth with 

 age. Utricles cylindrical, small, 500-650/t long, by 120-170 (rarely to 220/*) 

 wide, apex usually distinctly thickened, blunt; smaller utricles sometimes 

 pointed, but never mueronate. Gametangia (?) small, 200-250 x 40-70/j ; 

 gametes 20-22 x 10-12/*. 



Habitat. — On rocks near low-watermark usually semi-exposed, or in deep 

 or shady rock-pools ; saxicolous or epiphytic : also in the sub-littoral region, 

 often on stipes of Laminaria Cloustoni. 



Season. — All the year round; many plants reaching maximum size in winter. 



In comparison with many localities on the south and east of England, 

 C. tomentosum is common in the west of Ireland. Very large plants were noted 

 in February, both in pools and from deep water. One specimen on Laminaria 

 Cloustoni measured a yard in length. In most cases the fronds are cylindrical, 

 but in some there is a marked flattening, especially in specimens washed 

 ashore from the sub-littoral region. 



The chief points of distinction between the present species and 

 C. mucronatum are (1) the slender branches (3-4 mm. thick), and (2) the 

 small utricles (500-650 /i long) (cf. figures 1-2 and 3-5, Plate 8). Further, 

 ft tomentosum does not assume a light green colour when growing in sunlight, 

 and it apparently reaches its maximum size during winter, at which season 

 ft mucronatum appears to be almost absent. The utricles moreover are often 

 thickened, but never mueronate. Both species are more or less tomentose, 

 but ft tomentosum more often so than ft mucronatum. 



C. mucronatum var. atlanticum var. nov. x (Plates VII and VIII, figs. 3-5). 



Plants robust, slightly branched, usually 6-9 inches high, rarely forming 

 large tufts 12-18 inches high, and much branched from below. Colour deep 

 green, bright green when growing in sunlight (due to the presence of bubbles 

 between utricles). Fronds robust, 5-7 mm. thick, entirely cylindrical (not 

 flattened below axils), dichotomous or dichotomously fastigiate, surface smooth 

 or slightly tomentose when young. Utricles very large, cylindrical or slightly 

 clavate, 800-1000/* long by 250-300/t wide, apex thin-walled, surmounted in 

 the younger parts of the frond by a small, sharp or blunt mucro, in the older 

 parts mueronate utricles often absent. Gametangia ( 2 ) large, 300-400 x 

 80-120/*. 



1 Var. atlanticum. Utriculi parte frondis adultiore laeves vel mitcrono brevissirne acuto aut obtnao 

 instruct!, parte junioie mueronati. 



