137 



Strommen (Inderoen), local but pretty plentiful, and at Munkholmen 

 and Roberg, scarce. 1 ) 



Lithothamnion evanescens Fosl. mscr. 



L. fronde Crustacea, subarcte adnata, superficie plus minusve 

 inaequali, rosaceo-violacea vel glaucescente, 1 — 2 mm. crassa, mar- 

 gine leviter crenato; conceptaculis sporangiferis sub foveola leviter 

 excavata 100 — 120 <x lata demum annulo distincto rotundato- 

 angulato circumdata immersis, diametro 200 — 250 />-; sporangiis 

 binas sporas foventibus, 130 — 160/* longis, 40—55 p. latis. Tab. 

 22, fig. 6—8. 



Description of the species. Of this plant I have seen but two 

 specimens, a Norwegian (fig. 7) and an American (fig. 6), the latter 

 gathered at Marblehead, Mass. Collin's coll. C. 



The crust is 1 — 2 mm. thick, rather irregular in outline and 

 not much decreasing in thickness towards the margin, and the 

 latter shallowly and irregularly crenate. In an older stage it is 

 rather easily loosened from the substratum. The surface is more 

 or less uneven, which partly is caused by covering up small extra- 

 neous objects, here and there, however, bearing small and irregular 

 excrescences, and the unevenness is also caused by the scars after 

 emptied conceptacles of sporangia being irregularly effaced. A small 

 part of one of the named crusts is provided with some few but 

 rather coarse, short and radiating striae, and the surface appears 

 in younger crusts to be feebly shining, in older, however, dull. 

 The colour is here and there a light rose pink with a violaceous 

 tinge, otherwise glouceous or yellowish. I have not seen new 

 crusts formed upon the primary. 



On a vertical section of the crust the cells of the upper thicke- 

 ning layer form straight or nearly straight rows, after decalcifying, 



*) After this was ready for the press I met with a sterile Lithothamnion in a 

 rather sheltered locality at Ytteroen in the inner part of the Trondhjem 

 Fjord, growing on stones or rocks just below low-water mark, which, no 

 doubt, also belongs to this species. It forms more extended crusts than 

 the above mentioned, but also here the surface is frequently somewhat 

 uneven, here and there with very small and irregular excrescences, and 

 occasionally I found new, smaller crusts formed upon the primary. 



