130 
3. Thallus a plate, originally one cell-layer in thickness but 
becoming several layered (1-5) in places by means of hori- 
zontal divisions ; cystocarps in raised pustules ; tetraspores in 
conceptacles.... aioe = 560 ... Melobesia ...p. 102 
Thallus a minute plate oer mm. in diameter) of two cell layers ; 
cells of underlying layer elongated in vertical direction, and 
each capped by a small cell of the upper layer; zonately 
divided tetraspores in conceptacles with an apical pore 
Dermatolithon ...p. 102 
Thallus many cells in thickness, sometimes differentiated into 
distinct strata with cells elongated in various directions ... 4 
4. Thallus encrusting or sometimes forming overlapping or even 
vertically arranged lamellae ; tissue showing curved zones in : 
vertical section (see fig. 110 in Hauck, p. 268) ; tetraspores in 
special marginal conceptacles with sieve-like apertures me 
Lithophyllum saps 
Thallus encrusting or forming coral-like growths; tissues in 
strata, of which the underlying is as in Lithophyllum, but the 
upper strata are composed of cells arranged in regular vertical 
rows (see fig. 112, Hauck, p. 272); tetraspores in groups 
superficially placed or only slightly sunk in the thallus 
Lithothammion ...p.103 
Thallus encrusting, of the same organisation as Lithothamnion, 
but with tetraspores in scattered groups deeply embedded in 
the tissues, conceptacles opening by sieve-like apertures 3 
Phymatolithon ...p.104 
eS 
oS 
5. Minute filamentous algae creeping in or on the walls of animals 
or other algae, rarely giving off upright free filaments except 
when reproducing ae = 1s arr Se cat a 
Minute plants forming extensive plates or stain-like patches 
on rock or other algae ; thallus an expanded basal plate from 
which arise vertical filaments of uniform height or a solid 
pseudo-parenchymatous mass ... sis ome ne Gay ae 
Thallus of various forms but neither encrusting nor endophytic... 10 
6. Thallus endozoic in the walls of Alcyonidium ; monosporangia 
on short free filaments emerging from the Alcyonidium wall 
Acrochaetium endozoicum ...p.78 
Thallus endozoic in Sertularia ; cruciately divided tetraspores on 
vertical filaments emerging through the Sertularia wall 
Rhodochorton membranaceum ...Pp.95 
Thallus endophytic in the walls of Cladophora rupestris, etc. ; 
tetraspores, often in twos, formed under the surface of the 
host wall; sometimes emergent Schmuitziella endophloea ...p. 102 
Thallus endophytic in the walls of various algae, forming a 
network ; reproduction by monospores cut off from cells of 
the filament; not emergent ... sists Colaconema ...p.77 
Thallus endophytic in the walls of Polysiphonie, etc., giving off 
monospores from emergent branches ... Acrochaetium ...p.77 
