A LIME-INCRUSTING ALGAL COMMUNITY OF A DANISH WELL 247 
vad the sédiments in contrary are formed of Dichothrix gypsophila 
(Kütz.) Born et Flah., and Phormidiiini laminosum, which are esti- 
inated to constitute together more than 85 per cent of the total con¬ 
tent of organisms. The stratigraphie sequence distinctly shows that 
the formation of lime incrustations there was commenced by Phor- 
midium laminosum, after which Dichothrix gypsophila appeared, 
succeeded by the other algal species listed below. 
As a rule, lime incrustations are described as rather poor in 
species (*), but in contrast to this, the comnuinity dealt with here, 
containing a total of 32 species, chiefly blue-greeh algae, must be 
characterised as fairly rich in sj^ecies. Of the species occiirring 
here besides Phormidiiim laminosum and Dichothrix gypsophila, 
aiso Aphanocapsa riinilaris, Calothrix fiisca, C. parietina, (^hroococ- 
cus turgidus, Gloecapsa aeruginosa, and Gongrosira incrustans were 
lime-incrustating, cf. Pia (1934, pp. 14-15), and these species must 
accordingly be regarded as native to the comnuinity. 
SURVEY OF THE SPECIFIE COMPOSITION OF THE 
COMMUNITY 
Cyanojihyceae : 
Aphanocapsa rîuularis (Garni.) Rabh.. cells 4-5.5 Calothrix 
fusca (Kütz.) Born et Flah., cells 7-7.5 C. parietina (Nag.) Thur., 
trichoine ca. 22 [x broad, cells ca. 9 u, sheath thick, interior brow- 
nish, exterior colourless. Chlorogloea microcystoides Geitler, cells 
ca. 2.5 JA, Chroococciis turgidus (Kütz.) Nag., Chroococcopsis gi- 
gantea Geitler, Dichothrix gypsophila (Kütz.) Boni..et Flah., cells 
6 a. broad, 6.5 jx long, sheaths 18-19 u, Gloeocapsa aeruginosa (Garni.) 
Kütz., cells ca. 2 .u, with the homogenous gelatinous sheath ca. 7 a, 
Microcystis parasitica Kütz., Petalonema crustaceum (Ag.) Kirchn., 
Phonuidium favosum, Ph. laminosum (Ag.) Gom., cells 1-1.5 [x, 
Plectonema piiteale (Kirchn.) Hansg.. sheaths ca. 3 a liroad, 'sery thiii 
and colourless, cell walls almost indistinct, the false raniifications 
not particularly short, lUunlaria Riasolcttiana Meiiegh., Sfigonema 
informe Kütz.. S. mesentericum Geitler, with sheath, cells ca. 35 jx 
broad, angular and very irregular. 
Ghloroiihyceae, etc. ; 
Grongosira incrustans Schmidle, Scenedesmus qiiadricauda Bréb. 
(1 spécimen), Spirogyra sp. (1 spécimen), Cosmarium sp. (l spéci¬ 
men), Trachelomonas sp. (1 specimen). 
Diatoms : 
(*) Tlius Fritsch (1949) writes that apart from the community-formiDg orga- 
iiisms, Pbormidiiim incrustatum and Schizothrix fasciculatiim, other algae than 
6'. puloinata, S. lacustfris, and C.bantransia stages of Batrachospermum are 
« only very occasionally présent and clearly constitute foreign includes. » 
