— 16 — 



Archaeolithothamnion (Rothpl.) Fosl. 1 ). 

 1 . A. Schmidt ii Fosl. mscr. 



Thallus forming crusts on Corals up to about 2 mm. thick, 

 sending forth crowded wart-like excrescences or short, simple or 

 subsimple branches about 2 mm. thick, occasionally up to 12 mm. 

 long, in an advanced stage frequently knotty and rugged and in 

 part rather anastomosing. Sporangia 50 — 65 p long and 30—40 // 

 thick. 



There are to be found two specimens of this characteristic species, 

 attached to about 15 cm. long and 3 — 5 cm. thick, somewhat compres- 

 sed pieces of dead Corals which it at length fully surrounds. The crust 

 does not attain any considerable thickness, apparently not exceeding about 

 2 mm., frequently thinner. It produces in a rather young stage numerous 

 small wartlike excrescences which little by little increase in size, becoming 

 more and more crowded , frequently at length forming short , simple or 

 subsimple branches 1.5—3 mm. thick, partly increasing in thickness up- 

 wards partly not, or with somewhat spherical thickened ends, occasionally 

 almost truncate, and in an advanced stage nearly always knotty and 

 rugged. The branches are up to 12 mm. long, but generally smaller, 

 in part at length rather anastomosing. New crusts sometimes are formed 

 upon the primary , or now and then stretched between the branches , or 

 irregular excrescences are formed by growing over extraneous objects. 

 The surface is feebly shining. The colour was in a fresh state a brownish 

 red, however almost discoloured in drying. 



On a vertical section the hypothallic layer is shown to be rather 

 feebly developed , composed of elongated cells which are up to about 

 20' ^ long. It sends forth perithallic rows the cells of which frequently 

 are IV2— 2 times longer than broad, or 11 — 18//. long and 7 — 10// 

 broad , here and there alternating with very small square or roundish 

 cells. Between the more or less densely crowded overgrown sporangia 

 (or cavities after these) the cells are as a rule much elongated and 

 narrow. 



The sporangia are formed in more or less regular sori up to about 

 3mm. in diameter. The sori are sometimes almost confluent, and ap- 

 pear especially in the excrescences or branches, being dissolved or nearly 

 so in the middle of February. On a section the overgrown sporangia 

 form rather regular layers over each other and parallel to the surface of 

 the frond. They are cylindric-bean-shaped or oblong, 50 — 65 // long and 

 30 — 40/7. thick, occasionally somewhat smaller and almost roundish- 

 ovate. 



The species reminds one in habit of Lithothamnion rugosum Fosl. 

 Otherwise it stands nearest to Archaeolithothamnion erythraeum (Rothpl.) 

 Fosl., from which, however, it seperates itself by essential characteristics. 



Picked up from a depth of ahout 5 fathoms off Koh Kahdat, apparently 



scarce. 



*) With regard to the limit of the genera I refer to Revised Systematical 

 Survey of the Melobesieae. Trondhjem 1900. 



