127 



younger specimens with any distinct whitish brim. Old specimens 

 appear to be more vaulted, which probably sometimes also is the 

 case in younger, as Solms Laubach remarks 1. c. „In der Jugend 

 ist er kreisformig und in Folge des in der Mitte rasen voranschrei- 

 tenden Dickenwachsthums ziemlich stark convex". The crust at- 

 tains a thickness of at least 1 cm. New crusts formed upon the 

 primary one are closely united to each other, and the limits are 

 difficult to detect, except when covering extraneous objects, which, 

 however, apparently not often infest this form. The surface is 

 frequently smooth, more seldom with local, scaly thickenings or 

 other local new formations, partly rather shining partly not. The 

 four-parted sporangia, of which I have seen but few, appear to be 

 about 100 — 120 //. long and 30 — 50 /* broad. Overgrown con- 

 ceptacles sometimes are numerous sometimes very few, almost 

 spherical and about 200 [i in diameter. Some specimens gathered 

 at Mandal on the south coast, also bearing conceptacles of spo- 

 rangia, most of which are emptied and the whole roof having dis- 

 appeared, partly accord with this form (cp. pl. 18, flg. 11) partly 

 form transitions to f. Harveyi. 



The plant recorded by Harvey 1. c. under the name of Mélo- 

 besia polymorpha also has been one of the doubtful forms, which 

 by Areschoug as well as some recent authors is referred to L. 

 polymorphum. As before remarked there is no authentic specimen 

 of Harvey's Lithothamnia in existence. I got, however, some spe- 

 cimens from Mr. B at ters, gathered at Cumbrae and considered 

 by him to be identic with Harveys plant, which without any 

 doubt really is the case However, Harvey referred all the crust- 

 like forms known to him to the same spedes, as he remarks him- 

 self, and among these probably also the true L. polymorphum. 

 Cp. Phyc. Brit. and Man. 1. c. But, on the other hand, the flgures 

 in Phyc. Brit. as well as the description of the reproductive organs 

 refer to the form in question. He describes the conceptacles such : 

 „Ceramidia minute, dot-like, sunk deeply in the outher layers of 

 cells, extremely numerous and often punctuating over the whole 

 surface of fertile fronds as if they had been closely marked with 

 pin-holes". There can be no doubt that this refers to the con- 



