170 



of July the conceptacles recently were emptied, and in the middle 

 of December provided with sporangia. On the British coast it 

 bears such ones in February. Specimens collected at Helgoland 

 in January, March, June and July partly bear sporangia partly 

 emptied conceptacles. 



Relation to other spedes. The plant appears to show greatest 

 affinity to L. circumscriptum, from which it, however, is easily 

 distinguished by essential characteristics. It sometimes approaches 

 L. polymorphum f. papillata in habit (cp. pl. 17, fig. 23), but the 

 latter is never smooth or only a part of the crust. 



Occurrence. Found at Drobak (Gran) and Nesodden (Schrei- 

 ner) in the Christiania Fjord, apparently rare. 



Geogr. Distribution. Helgoland (Kuckuck); Britain (B at ters); 

 the Atlantic coast of North America (Collins). 



Lithothamnion scabriusculum Fosl. mscr. 



L. fronde crustacea, 0.1—0.3 mm. crassa, scabriuscula, arcte 

 adnata, vinacea. Tab. 22, fig. 9. 



Bemark on the spedes. Some years ago I collected in the 

 most eastern part of Finmarken a sterile specimen of a Lithotham- 

 nion which seems to represent the type of an undescribed species. 

 I then sent it to Prof. Kjell man if he might have seen a similar 

 one. However, he declared it to be a specips unknown to him, 

 and together with some other doubtful algæ I left it unrecorded 

 in Contrib. I. Although sterile, there can be but little doubt that 

 it forms a separate species, if not, perhaps, by closer examination 

 of larger and fertile materials proving to be a form of L. lævigatum. 



JQescription of the spedes. The plant forms a thin, scarcely 

 more than 300 /x, partly only 100 fi thick and somewhat extended 

 crust on a stone, composed of some confluent primary crusts, 

 with the limits sometimes visible sometimes not. It elings closely 

 and very firmly to its substratum, plainly decreasing in thickness 

 towards the periphery, and the very thin peripherical portion scar- 

 cely perceptibly zonated. The margin is shallowly and irregularly 

 crenate and lobed. The surface is somewhat uneven partly in 

 consequence of small, scaly thickenings, which are a little larger 

 than in L. lævigatum partly also by growing over -small extra- 



