146 Dansk Botanisk Arkiv, Bd. 3. Nr. 1. 



8. Peyssonnelia (Eupeyssounelia) rubra (Grev.) J. Ag. 



J. Agardh, Spec. Alg. II, 1851, p. 502, Epicr. Flor. 1876, p. 386. De 

 Toni, Syll. Alg. vol. IV, sect. IV, 1905, p. 1696. 



Zonaria rubra, Greville in Linnean Transact. XV, prt. 2, p. 340. 



After some hesitation I have named two specimens in Dr. 

 Borgesen's collection as P. rubra, though Schmitz^) doubted of 

 the occurrence of P. rubra in a tropical sea and though, according 

 to J. Agardh, P. rubra should be limited to the Mediterranean. 

 J. Agardh describes the frond of P. rubra as "membranacea" but 

 the carbonate of lime incrustated between the rhizoids and in the 

 basal mucuous layer makes the plant very brittle and calcareous. 

 I could detect no difference between specimens from Naples, 

 Genoa, Antibes and those from the West Indies. The latter are 

 perhaps a little more delicate and orbicular, not so profoundly 

 lobed as the Mediterranean species can be. 



Found at St. Croix, White Bay, shallow water, (No. 1546 n 1585 H). 

 Dry specimens. 



Another specimen (No. 2034) found at St. Jan, off America Hill in 

 a depth of about 15 fathoms, is distinguished by its light, pink colour and 

 thin thallus from P. rubra. Its ascending filaments, seen in longitudinal 

 direction, run more obliquely and the first cell of the perithallus is higher 

 than is usually the case in P. rubra. This alga stands between P. rubra J. 

 Ag. and P. Gunniana J. Ag. I hope that future explorers of the West- 

 Indian region, with more material at their disposition, will shed further light 

 on the systematic position of these confusing membranaceous species and 

 will settle my doubts about P. simulans, whether it is a new species or 

 to be sunk in P. conchicola. I felt, while working out this collection, 

 that to know the limits of a species, one must first distinguish, in order to 

 be able to unite afterwards and that for the present I could only distin- 

 guish and had no right to unite. 



Fam. 4. Hildenbrandiaceæ. 

 HildenbrandiaM Nardo. 



1. Hildenbrandia prototypus Nardo. 



Nardo, I., in Isis, 1834, p. 675 [Hildbrandtia). Hauck, F., Meeres- 

 algen, p. 38. 



1) Schmitz, Marine Florideen von Deutsch Ost-Afrika, Engler's bot. 



Jahrb., 1895, p. 172. 

 ^) Regarding the spelüng of the generic name compare the foot note in 



Engler u. Prantl., »Die Natiirl. Pflanzenfamihen« , I. Teil, Abt. 2, 



p. 544. 



