ADDENDA. 



P. 82, before Genus XIII., insert 



OMPHALODIUM (Mey. & Flot.) Koerb. 



Apothecia scutellaeform, much as in Parmelia. Spores 

 ellipsoid, simple, colourless. Spermatia short-acicular ; on 

 sub-simple sterigmas. Thallus sub-monophyllous and stel- 

 late-lobate, attached to the substrate at a single point, by 

 a disk-like process, in the manner of Umbilicaria. 



0. Arizonicum-, thallus ample; coriaceous j becoming wrink- 

 led, and ridged ; greenish-yellowish ; beneath black, reticulately 

 ridged and thickly besprinkled with black tubercles, and the 

 ridges passing also into ragged extensions; apothecia ample, 

 a little elevated ; disk dark-chestnut ; the margin finally flexu- 

 ous and sub-crenate. Spores (in 8 s , in veutricose thekes, among 

 agglutinate paraphyses) ellipsoid, liinbate, colourless, ~ mic. 



Upon rocks, Santa Rita Mountains, Arizona, Mr. C. G. 

 Pringle-, comm. Sprague. Thallus exceeding at length three 

 inches across ; and the apothecia from two reaching more than 



eight mic., in width. Omphalodium (upon which the author's 



Gen. Lich. p. 28, may be compared) is a group constituted of a 

 South African lichen 0. Hottentottum (Ach.) Flot., and a 

 Peruvian 0. Pisacomense, Flot. Our plant is very near to the 

 former of these ; differing especially in its wider lobation, and, 

 so far as can be judged from the descriptions and specimens, 

 the brighter colour of its thallus, the less entire apothecia, and 

 the larger spores. The fibrils of the under side, and of the 

 exciple, which are so marked a feature of 0. Hottentottum, are 

 indeed quite deficient in the American lichen, but they are 

 wanting sometimes in the African (Delis. Stict. p. 136) and their 

 place is taken in ours by tubercular processes exactly like a com- 

 mon anamorphosis of the fibrils in Umbilicaria vellea, and U. 



Dillenii. The disappearance of the fibrils of one form in the 



processes just referred to of another, the passing of the ridges 



