No. 3] NEW OR CRITICAL CALCAREOUS ALGÆ. 31 



some of the calcareous algæ which underlie Harvey's descriptions. 

 The result of these investigations shows, that L. calcareum Harv. 

 is a true Litliothamnion, while on the other hand L. fasciculatum 

 in the sense tåken b}^ Harvey is a true Lithophyllum. These 

 two spedes are in fact rather eas}^ to separate even in a sterile 

 state. But L. fasciculatum and certain forms of the below men- 

 tioned L. dentatum are sometimes extremely difficult to distinguish. 



The above f. incrassata corresponds in the main with the 

 qaoted figure in Harv Phyc. Brit. This form appears hov/ever to 

 be rather scarce. It passes into f. divaricata which characterizes 

 itself by the more or less spreading and not or but in part fasti- 

 giate branches, which moreover often are more or less atienuating 

 with rounded tips. This two forms are analogous to Litliotham- 

 nion topJdforme f. globosa and f. typica. 



The form eunana is most nearly related lo f. divaricata, but 

 is scantily branched or simple, and much smaller. 



A delicate form of the species is f. subtilis, characterized by 

 its thin branches partly attenuating partly an more frequently thicke- 

 ned upwards, truncate and moreover often depressed in the centre, 

 or ending into a more or less expanded disk depressed in the centre, 

 or dentate and nearty funnel-shaped, or sending forth a mumber 

 of Short and nearly verticillate branchlets. This form is ve\y varying, 

 and it even approaches certain forms of the foUowing species. 

 Characteristic specimens have been tåken in Fahy Bay, Ballinakill 

 Harbour, on muddy bottom together with other algæ in 1 — 1^2 

 fathoms water by Mr. Henry Hanna. Is is also known from 

 Roundstone. Cp. 1. c. 



The form compressa on the one side stand nearest to f diva- 

 ricata, but difiers by its in the upper part compressed, sometimes 

 even broad branches and then so much approaching the following 

 species that a certain limit is difficult to draw. 



1 have hitherto but seen certain specimens of this species from 

 the west coast of Ireland. 



Lithophyllum dentatum (Kiitz.) Fosl. 



List of Lith. p. 10; Spongites dentata Kiitz. Polyp. calc. p. 33. 

 Lithothamnion dentatum Hauck, Meeresalg. p. 273. 



