(213) 
L. E. p. 417. Mey. Entwick. p. 325. Mont. Pl. Cell. Cub. p. 160; 
Crypt. Guy. p. 58; Syll.p.356. Scher. Enum. p. 226,t.8,f.6. Leight. 
Brit. Anz. Lich. p. 24, t. 8,9. Norm. Con. p. 27. Tul. Mém. Lich. 
p. 184, t. 10, f. 24-27. Nyl. Enum. Gén. 1. c. p. 134; Lich. exot. 1.c.; 
in Prodr. N. Gran. p. 109, t.2, f£.51; Syn. Lich. N. Caled. p. 66. Th. 
Fr. Gen. p. 96. Stizenb. Beitr. lc. p.152. Trypethelii sp., Ach. in 
Act. Gorenk., cit. ipso. Chiodecton, Melanodecton, & Leucodecton 
pr. p., Mass. Ric. p. 149; Esam. p. 43. 
Apothecia rotundato-difformia oblongave, plano-convexa, immar- 
ginata, hypothecio nigricante suffulta, in stromate albo imimersa. 
Spore fusiformes 1. nunc oblongo-ovoidex, quadri-pluriloculares, 
rarissime muriformi-multiloculares, fere semperincolores. Spermatia 
acicularia; sterigmatibus simplicibus. Thallus crustaceus, uniformis. 
The systematic perplexities involved in the natural relation of Graphis 
tricosa to Glyphis remain now as great as they were when Acharius con- 
sidered them; being by no means removed by Nylander’s acute distri- 
bution, between Graphis and Glyphis, of what were once certainly reckoned 
varied forms of the lichen first named. It appears to be out of the ques- 
tion to frame a character for Glyphidei which shall exclude Medusula ; 
and equally impossible to exclude the Medusuline type from the circuit of 
variation of Graphis dendritica. But whatever the difficulties of Glyphis, 
Chiodecton is too closely akin wholly to escape them; and isitself, whether 
simulating Platygrapha, or developing into Medusuline forms, or now 
almost suggesting (as to Acharius) Trypetheliine ones, one of the best- 
marked types of Graphidaceous lichens. 
Acharius did not recognize any proper exciple in Chiodecton or in 
Glyphis, but-his description of the apothecia (Monogr. l. c., pp. 37, 44) at 
least opens the way to such inference, and it is perhaps too much to say, 
with Eschweiler, that he ‘wholly overlooked the structure.’ The latter 
author was yet first to indicate (Syst. p. 19) that Glyphis agrees with all 
typically developed Graphidacei in the possession of a distinct exciple ; 
though he considered this to be only represented by a hypothecium in 
Chiodecton. But the microscope scarcely confirms the asserted structural 
diversity of the latter; and it may be said to be, in this respect, chiefly 
distinguishable by its almost always plano-convex thalamia being immar- 
ginate ; while the concave or channelled exciples of Glyphis may be said 
to be margined. And when Chiodecton offers, as in C. seriale, perfectly 
flat, or even impressed hymenia, it is not always easy to distinguish it from 
Glyphis labyrinthica by any prominent, external difference in the excipular 
envelope. 
In the great majority of species of Chiodecton we find fusiform spores, 
with the spore-cells of such spores, as they occur in the colourless series ; 
and, with one exception (in C. Feei, Meissn.) Fée describes no other type. 
‘A peine peut on découvrir, says this writer, ‘dans ces organes de légérez 
