32 M. FOSLIE. [1899 



f. aemulans Fosl. mscr. 



L. dentatum Hauck 1. c. t. II, fig. 2. 



f. gyrosa Fosl. 



L. fascicalatuni f. gyrosa Fosl. On some Lith. p. 8. 



f. dilatata Fosl. 



L. fasciculatum f. dilatata Fosl. 1. c. 



f. Macallana Fosl. mscr. 



Lithothamnion agariciforme (iVI'Calla?) in herb. Sc. et Art Mus. Dublin; ex parte. 



In places where the present spedes grows gregarious with 

 Lithopliyllum fasciculatum, the limits between these two species 

 are extremely difficult to dravv. It does not seem to be debarred 

 that we have here hybrids developed from two in their typical 

 forms so different species. In one of the localities at Roundstone 

 mentioned in Irish Natur. 1. c, both species grow together in 

 abundance, although L. fasciculatum frequently in greatest number 

 of individuals, partly and most commonly shovving vvell developed 

 and easily recognized specimen of the one or other species, partly 

 how^ever specimens to be seen v^hich appear to partake of the 

 characters of both. Sometimes specimens of both species are ana- 

 stomosed, with a rather distinct limit, sometimes however looking 

 like a solitary individual, but with characters now peculiar to the 

 one now to the other species. This is on the one side due espe- 

 cially to L. fasciculatum f. compressa and on the other hand f. 

 aemulans of the present species. The latter likely seems to be 

 the typical form of this species, nearly as represented in the quoted 

 figure by Hauck. It is however much varying, partly with 

 shorter and narrower branches, on the one side approaching L. 

 fasciculatum f. compressa, and on the other showing transitions 

 to f. Macallana, but partly with much broader branches than in 

 the said figui-e, and then even much approaching Lithophyllwii 

 decussatum. Besides it passes into f. gyrosa which represents a 

 characteristic form, with plicate, depressed-emarginate, fastigiate or 

 nearly fastigiate branches. The figure formerly referred to as re- 

 gards the latter form, Harv. Phyc. Brit. pl. 74, fig. 2 (M. fasci- 

 culata), does not , represent a typical specimen of this form, but 

 approaches those not unlikely h^^bridous specimens. Therefore, I 



