219 
This species occurs on stones and rocks, and on shells of molluses (Mytilus, 
Modiola, Trochus, Littorina), from ordinary water-mark to 19 meters depth. Almost 
all the specimens belong to f. {ypica, a few only have been referred by Fosrie to 
f. sublevis, which differs by smoother surface and less crowded sporangial concep- 
tacles. It was rather surprising to me to find the species growing at low-water 
mark on the granitic rocks of Bornholm, where the salinity of the water is about 
7—8 "loo only. It was here fairly typical though sterile, and with numerous adven- 
titious fronds, and occurred in fairly great numbers. In the other locality in the 
Baltic (RG), only sterile but rather large crusts were found. 
Ripe sporangia have been met with in July (partly together with undivided) 
and September. Antheridial conceptacles with spermatia were found in July and 
September, and ripe cystocarpic conceptacles in July. 
Localities. Ns: Thyboren, groin no. 58, stunted specimens. — Lf: Sondre Ron by Lemvig; 
Thisted harbour (!, C. H. Ostenfeld); Sallingsund (Th. Mortensen); LS!, off Bjorndrup, east of Mors, 5,5 m. 
— Kn: Frederikshavn, at low-water mark; Trindelen, 15 m (small spec.). — Ke: EU, Lille Middelgrund, 
14 m (small specim.); IA, Store Middelgrund, 16 m. — Ks: Oure Sund; Bramsnæs Fjord. — Lb: At 
Lyngsodde off Middelfart, 15—19 m, large fertile crusts. — Sb: GP, at Halskov Rev, 9,5—11,5 m; Aver- 
nakhage by Nyborg, low water. — Sm: VC, Venegrund, 3—5,5 m. — Su: TF”, Staffans Flak, 11—13 m; 
PS, off Charlottenlund, 5,5 m. — Bm: RG, 6 miles N.N.W. of Falsterbo lighthouse, 11,5 m. — Bh: Hellig- 
domsklipperne, Ro, Bornholm. | 
3. Lithothamnion Sonderi Hauck. 
Hauck, Meeresalgen, p. 273, Taf. III, fig. 5; Foslie, Norweg. Forms, 1895, p. 127; Heydrich, Lithoth. Helgol., 
1900, p. 77, Taf. II fig. 20—22; Foslie, Remarks, 1906, p. 23; Lemoine, Structure, 1911, p. 96. 
Though this species has been met with in a number of different localities in 
the Danish waters, it has in most cases been found only in small quantities together 
with other species. I have therefore only little to communicate with regard to it, 
but must refer to the descriptions of Hauck, FosLıE and Mme LEMOINE. 
As pointed out by Fosrıe and Mme LEMOINE, the hypothallium is feebly devel- 
oped. According to the last-named author it consists only of a single layer of cells; 
“les autres se relèvent très rapidement pour former le périthalle”. The ascending 
filaments may, however, rise more gradually, and the hypothallium may then con- 
sist of two or three cell-layers (fig. 136 B). The hypothallic cells measured 5—7 yz 
broad, 15—21 » long; those of the vertical filaments I found to be 3,5 -7 x broad, 
5,5— 11, long. These measurements are somewhat smaller than those of Fosrie 
and Mme Lemoine. Transverse fusions between the cells are very frequent in the 
perithallium. In sections stained with hæmatoxyline the middle lamellae are very 
distinct. In the same sections the horizontal limiting lines are intensely stained; 
their course is somewhat irregular (fig. 136). Older crusts may have a considerable 
number of layers. The cells of the under part of the frond are often filled with 
and characterized principally by cytological statements relating to the development of the cystocarp. 
These statements are, however, very insufficiently supported, and I have had no opportunity of veri- 
fying them. 
28* 
