Mr. W. II. Harvey on a new Alga from the coast of Ireland. 27 



Length of recent* ovum of Scyllium Catulus ? 4 inches 6 lines ; 

 breadth 1 inch 9 lines ; depth 3 — 4 lines ; surface smooth or plaited 

 transversely ; sides very strong and closely plaited throughout ; ten- 

 drils very strong. Colour a uniform brown, but differing in shade 

 in different ova. 



Belfast, May 1844. Wm. Thompson. 



IX. — Description of a minute Alga from the coast of Ireland. 

 By Wm. Henry Harvey, Esq. 



[With a Plate.] 



Rhododermis, Harv. MS. 



Gen. Char. — Frons carnoso-membranacea, expansa, Crustacea, 

 facie inferiore adhserens, e cellulis polygonis sanguineis minutis for- 

 mata. Fructus ? verruca? pertusse in frondem sparsae. 



R. Drummondii, Harv. MS. 



Hab. At New Castle, co. Down, spreading over the rocky sides 

 and bases of maritime caves, in places where it is covered by the sea 

 at high water, but exposed, on the ebb of the tide, to the dripping 

 or trickling of fresh water. Dr. Drummond, May 1840. 



Frond spreading in wide, concentric, but not regularly circular 

 patches of a dark blood or brick-red colour, when dry purplish 

 lake, closely adhering to the rocks on which it grows, and to 

 which it is attached by the whole of its lower surface ; of a fleshy- 

 membranous, very tenacious substance, glossy, about half a line 

 in thickness in the centre, but becoming gradually thinner to- 

 ward the margin, composed (as shown by the highest power of 

 the microscope) of strata of minute polygonal cellules closely 

 packed together, and filled with brilliant rosy endochrome. The 

 surface appears marked with wavy interrupted lines, and more or 

 less thickly furnished with wart-like dark-coloured tubercles, 

 which are either scattered or grouped together in linear masses. 

 These tubercles are hemispherical, prominent, of the same struc- 

 ture as the rest of the frond, deeply coloured at the margin, but 

 in the centre colourless, and generally pierced by a hole which 

 goes through the frond. It is doubtful whether they contain the 

 fructification. Dr. Drummond was not able to discover sporules 

 in any of them in the recent plant, nor have I been more fortu- 

 nate with the dried specimen. In outward aspect they much 

 resemble the fruit of Grateloupia, but a minute examination shows 

 them to be invariably empty. 



Though undoubtedly of marine origin, the presence of some 

 fresh water in the absence of the tide seems favourable to the 

 growth of this Alga, as Dr. Drummond observed the colour to 



* The specimens have dwindled in drying to about one-half their original 

 size. 



