KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 20. N:0 5. 97 



Lithothamnion inter medium nob. 



L. fronrle subglobosa, dilute rosen, scabriuscula, diametro circa 7 cm., parte centrali solida, plus minus 

 distincte lobata, ramos vel breves, verrucfeformes vel longiores usque 4 — 5 mm. altos, basi 2 mm. crassos vel 

 simpliees, conico-cylindricos, apicibus obtusis, vel iiifra apioera uno alterove ramulo brevissimo, verrucseformi 

 proeditos uudique emittente; coneeptaculis sporangiferis demum innatis, raiimtis, convexiusculis at parum promi- 

 nentibus, oreberrimis, nuUo ordine in tota fronde sparsis; sporangiis quaternas sporas foventibus, 1.30 — 150 //. 

 longis, circa 40 (.i. crassis; Tab. 4. 



Descriptiön of the species. External shape. The plant forras spherical or spheroi- 

 dical balls, wliich, when older, are about 7 era. in diameter (fig. 1). In several of the 

 specimens examined by rae there was nothing included in the interiör of these globular 

 masses; others encompassed small stones. The frond is constituted of a thick central con- 

 tained portion intersected with cavities and canals, and projecting in more or less distinct, 

 simple or divided, clurasy, thick lobes. These carry partly simple, short, and wart- 

 like, partly longer and branch-like processes. The latter reach a length of 4 — 5 ram., 

 with a diameter of about 2 min. at the base. They are sometiraes simple, conically 

 cylindrical, obtuse, sometimes furnished with one or two, generally short, wartlike side- 

 branches below the tip. The plant is more or less deeply rose-coloured. Its surface 

 is uneven, on account of local, scaly thickenings of the surface. As in the preceding 

 species, the central mäss is rich in holes after boring-muscles, and in passages produced 

 by worms. 



Structure of the frond. The fracture is white or faintly rose-coloured Avith rare^ 

 small, yellowish-brown döts — the grown-in conceptacles of sporangia. In longitudinal 

 section the processes show distinct cup-shaped layers, although these are not so re- 

 gular as for inst. in L. soriferum. The inner cells of these layers, in longitudinal section, 

 are rectangular with rather thin walls, the outer ones have more rounded cell-rooms 

 and somewhat thicker walls. The diameter of the former amounts to 7 ,«., their 

 greatest length to about 15 jn. fig. 8. A cross cut of a process shows essentially the 

 same structure as in the preceding species, difFering only by the cells of the outer 

 concentric layers having thinner walls and a greater length in the direction of the 

 radius (fig. 4, 6, 7). The surface cells of the frond are isodiametrical in a tangential 

 section, 4 — 6-angular, about 10 ,«. in diameter, with walls 2,:) /u. thick (fig. 9). 



Organs of projjafjation. The conceptacles of sporangia are spread över the whole 

 frond and become grown över in the present species as in the preceding. Although 

 there are certainly found older grown-in organs of this kind nearer the centre of the 

 processes, raost of them are peripherical. The superficial ones are but little prominent 

 above the surface of the frond, small, with slightly convex roof (fig. 3). This is tra- 

 versed with nnmerous gelatiniferous canals. In none of the specimens examined I have 

 seen these reach to the surface of the roof, and from that cause do not know how 

 their orificial cells may be constructed. The sporangia are tetrasporic, spindleshaped- 

 cylindrical or claviform, 130 — 150 ,u. long, about 40 ,«. thick (fig. 10). 



Relation of the present species to others. The present species is probably most 

 closely related to L. glaciale. By its general habit and its grown-in sporangia, it re- 

 minds one most of this. In other respects, however, its structure approaches more 



K. Vet. Akad. Handl. Bd 10. N:o 5. lo 



