— IA. x 
THREE NEW MARINE ALGA. 453 
the paraphyses, and there is never any clearly marked line of 
separation between them as in R. clavata. When fresh the sori 
of both species are fleshy, and slightly raised above the surface of 
the frond, but when allowed to dry they shrink considerably 
more than the rest of the plant, which causes them to crack all 
over; but as both species, so far as I have observed, grow under 
water, this can very seldom happen naturally. I am indebted to 
Prof. Farlow, of Harvard College, for American specimens of 
R. clavata, and also for valuable notes on the affinity of the 
species. 
Even the genus to which this interesting alga belongs appears 
doubtful. Dr. Bornet and Prof. Agardh consider it a true 
Ralfsia, but, on the other hand, Dr. Kjellman thinks it is more 
nearly related to Lithoderma or Stragularia, and Dr. Hauck 
would place it and Myrionema Henschii in a new genus. 
The sporangia are usually attached at the base of the para- 
physes, but not unfrequently they appear to be terminal on the 
vertical filaments (see Pl. XVII. fig. 21), as in Lithoderma, calling 
to mind the passage in Areschoug's description of that genus, 
where he says: “ Utraque fructificatio, in diversis plantis, filisque 
verticalibus quorum cellule apicales longe sunt product, cir- 
cumdata.” It thus forms a link between the Ralfsiacee and 
Lithodermacee. 
EXPLANATION OF PLATE XVIII. 
Phyllitis filiformis, figs. 1-6. 
Fig. 1. Plant, natural size. Figs. 2,3. Roots, x 300. Fig. 4. Portion of frond 
with plurilocular sporangia, x 300. Fig. 5. Section of frond, X 
300. Fig. 6. The same, x 600. 
Ectocarpus Holmesii, figs. 7-16. 
Fig.7. Plant, natural size. Fig. 8. The same, from Minehead, x 150. 
Figs. 9-12. Specimens of plurilocular sporangia, x 600. Figs. 13- 
15. Unilocular sporangia, x 600. Fig. 16. Distorted cell, x 600. 
. Ralfsia spongiocarpa, figs. 17-21. 
Figs. 17, 18. Plant, natural size, in situ. Fig. 19. Sporangium and paraphysis, 
X 600. Fig. 20. Branching vertical filament, x 600. Fig. 21. 
Terminal sporangium, x 600. 
! Ralfsia clavata, Crouan, fig. 22. 
Fig. 22, Sporangium and paraphysis, x 600 ; for comparison with the foregoing. 
