82 



f. irregularis Fosl. mscr. 



f. tuberculis fere hemisphsericis vel irregularibus, plus minusve 

 laxe dispositis. Tab. 18, fig. 6 — 9. 



Syn. Lithothamnion polymorphum Kjellm. N. Ish. Algfl. p. 134 (102); ex parte. 



sec. spec, ab auct. determ. 

 „ „ Kleen, Nordl. Alg. p. 11; ex parte? 



„ „ Fosl. Contrib. I, p. 9. 



Description of the species. As remarked below under L. 

 polymorphum I consider the present plant an independent species. 

 It forms incrustations on rocks. The form of the crust partly 

 depends on that of the substratum, to which it clings closely and 

 at first firmly, but when older at least often is easily separated 

 from it. In f. verrucosa the crust puts forth more or less clumsy 

 protuberances or lobes, or such are formed by covering up extra- 

 neous objects, and bearing, like the rest of the crust, numerous 

 wartlike knobs up to about 2 mm. high and 0.5—2 mm. thick, 

 with in general blunt apices. PI. 18, fig. 1 — 5. In the form irre- 

 gularis the crust is more or less irregular, and it is furnished with 

 less numerous or few wart-like knobs, but more often smaller or 

 larger subhemispherical or irregular processes. PL 18, fig. 5 — 9. 

 Upon the primary crust new crusts are formed partly clinging to 

 the subjacent one partly rather elevated and here and there free, 

 or covering extraneous objects, or new, local crusts are formed 

 so as to cover the numerous animals frequently living on or pene- 

 trating the plant, and the marginal portion of these new forma- 

 tions may sometimes be more or less free, or they form lamels, 

 or ridges, or in all very irregular processes. PL 18, fig. 7 shows 

 a specimen with in part small lamels. The crust attains a thick- 

 ness of up to nearly 1 cm., frequently, however, less. Old indi- 

 viduals occasionally are to be found nearly free on the bottom, 

 or become loosened by external causes. Such loosened individuals 

 continue their growth and new formations are partly formed on 

 the lower side turned towards the bottom, which, however, is also 

 the case in fastened but nearly free individuals. Younger speci- 

 mens are feebly shining, older ones often finely rugged on the 

 surface. The plant is furnished with short and very fine striae in 



