203 



4. OMPHALARIA Dur. et Mont., Orb. Diet. 7: 351. 1849. 



Considerable uncertainty exists as to the limitations of this genus, 

 caused by the variability of the apothecial and spore-characters, and 

 to a lesser degree by the changes in the algal symbiont. 



In this group the thallus has a decided fruitcose tendency. The 

 lobes become broad and irregularly branched in the higher forms, 

 closely resembling, in external appearances, some of the lower Colle- 

 mas. In the lower forms the thallus is small, sparingly branched, 

 with short nearly cylindrical lobes ; these, with their terminal, nearly 



J J / 



globose apothecia, closely resemble Lichina, from which this group 

 is probably phylogenetically derived. 



There is no cortical tissue, not even in the highest forms ; the 

 outer thin conglomerate layer consists of shriveled hyphae and dead 

 algal cells, similar to that in Lichina ; this is followed by the algal 

 layer, which consists of hyphal branches, much interwoven and for 

 the most part extending vertically to the outer surface ; the individ- 

 ual algal cells closely resemble those of Lichina, so that superficial 

 examination is apt to lead to mistaken conclusions. In Ri-cnJaria 

 the entire algal chain is enclosed by the gelatinous layer. In the 

 algae of Omphalarta each cell is enclosed by a gelatinous layer. 

 From this it is evident that the algae are not Rivularia nit i da, but 

 some species of Gloeocapsa, perhaps G. polydermatica, though much 

 larger than the form occurring in Baeomyces roseus (hypernutri- 

 tion). Sometimes it also happens that Nostoc occurs in the same 

 thallus with Gloeocapsa. 



The central portion of the thallus, especially in lower forms, is 

 occupied by the hyphal bundle, which is, however, not sharply 

 demarcated from the algal layer. The hyphal branches extend 

 longitudinally, giving off numerous lateral branches. The color of 

 the thallus is very dark, in fact of about the same color (and con- 

 sistency) as that of the CoUcmas. 



The apothecia are rarely numerous, terminal, globose, often 

 wholly wanting ; at the beginning soon becoming more or less cup- 

 shaped. They resemble very closely the apothecia of Lichina. 

 Sometimes the hypothecium as well as the greater portion of the 

 thecium is dark in color; again these structures appear colorless. 

 The thecium and upper ends of the paraphyses are always dark 

 in color. The spores also seem to be variable ; in the ma- 

 jority of species they seem to be simple, colorless, and elliptical ; 



