No. 5] NEW OR CRITICAL CALCAREOUS ALGÆ. 29 



As remarked in Some new or er. Lith. p. 17 the present 

 species is much varying, but the forms run into each other so 

 that any limit frequentty is difficult or impossible to draw, the 

 variation generally being consequent only to local conditions. 



The obove quoted f. incrassata is however one of the more 

 characteristic forms of the species. It forms thick crusts propably 

 on rocks or stones, with coarse, wartlike or lumpy, crowded lobes, 

 or blunt branches increasing in thickness upwards and occasionally 

 attaining a height of up to about 1.5 cm. by nearly the same 

 thickness. In structure it differs from the other forms quoted, the 

 cells of the perithallic layer frequently being a little larger. Other- 

 wise it stands nearest to f. angulata but also showing some relation 

 to f. Harveyi. It is probabty the same form recorded by Harvey 

 1. c. from Algoa Bay. I have specimens from the Cape of Good 

 Hope, kindly communicated by Dr. H. Becker, but the locality 

 is unknown. 



I do not adopt three forms of this species described by Hey- 

 drich in Ber. d. deutsh. bot. Ges. Bd. 17, p. 225 under the names 

 of f. jiabellata, f. subdichotama and f. lahyrintJiica, as they in my 

 opinion belongs to forms formerly known, or not being so charac- 

 teristic that they ought to be denominated as separate forms. 

 Thus f. flahellata is in fact as Heydrich remarks himself „eigent- 

 lich weiter nichts als eine f. depressa, von der zwei Exemplare an 

 einander fåcherformig und horizontal emporwachsen". I have seen 

 this formation from several places. and especially met with it on 

 the west coast of Ireland where L. incrustans is very abundant, 

 fringing the rocks in the lower part of the litoral region, surroun- 

 ding stones or shells almost everywhere in exposed places, or 

 covering the bottom of rock-pools even in the upper part of the 

 litoral region. In the latter places f. depressa especially is to be 

 found. It often entirely covers the bottom of large but generally 

 shallow rock-pools with a nearly smooth and uniform layer, but 

 just below the surface of the water the pools often are fringed 

 with the most curious forms of the species. So especially if there 

 are even small projecting parts of the bottom or other objects, 

 and when two crusts here trumble they grow together and at 



