No ol NEW OR CRiriCAL CALCAREOUS ALG.E. 33 



referred this form 1. c. to L. fasciculatum, ' while it in fact be- 

 longs to L. dentatum. 



The forms dilatata Qx\å. Macallana' siscdås near to each other. 

 The former attains a diameter of 10 cm. by a thickness of about 

 2 cm., and the latter chiefly differing by forming roundish or 

 slightly compressed, often hollow balls up to 12 cm. in diameter, 

 the irregular branches resembling those in f. dilatata, but frequently 

 more upright. The form Macallana is only known form M"Calla's 

 collections from Roundstone, and has not at least in its typical 

 shape afterwards been found. This form now and then also shows 

 connection with f. gijrosa, but frequently being rather different. I 

 have even been in doubt whether f. dilatata and f. Macallana 

 really are forms of the present species, or in part perhaps repre- 

 sent h3'brids between L. fasciculatum and L. dentatum. However, 

 in structure they rather accords with the latter 'than otherwise. 



This species is known from the Adriatic, the eastern part of 

 the Mediterranean, and the west coast of Ireland. 



Lithophyllum decussatum (Ell. et Sol.) Phil. 



in Wiegm. Arch. 1837, p. 389; Millepora decussata Ell. et Seil. Zooph. p. 

 131, t. 23, flg. 9. Non Solms, Corall. Monogr. p. 14; Hauck, Meeresalg. p. 270; 

 Fosl. On some Lith. p. 5. 



f. typica. 



Melobesia decussata Aresch. in J. Ag. Spee. Alg. 2, p. 517; sec. spee. 



f. decumbens Fosl. mscr. 



Syn. Melobesia agariciformis Aresch. 1. cp. 516; sec. spee; excl. syn. 



The alga that I 1. c. referred to the species described by 

 Ellis and Sol and er 1. c. has in some respects and outward re- 

 semblance to certain forms of the species in the sense here tåken, 

 but the former is a Lithothamnion, while L. decussatum. as limi- 

 ted by Areschoug 1. c. is a Lithophyllum^ according to speci- 

 mens of the latter that I have afterwards seen. Consequently I 

 adopt the species as understood by Areschoug. especially as one 

 of the specimens in his coUection comes very near to the figure 1. c. 



I refer M. agariciformis Aresch. to the same species, also 

 according to a specimen in his collection. This is a form which 



