12 



afliftanee of any external procefs whatfoever, thus excluding even the Conjugate, 

 which it was his intention to admit. 



Mertensia. — Tubuli fub coriacei, Vitus articulati, fporulz in tunica, 

 fapillas Veficales clavatas fafciculatas eff.cicnte, fparfa. 

 This genus has but one fpecies, the Uloa lumbrlcalis of Linnaeus, a native of 

 the Cape of Good Hope, with which I am totally unacquainted. According 

 to Dr. Roth's account, the ftru£ture of this plant is extremely curious. The 

 filament 1 ; are lined on the infide with a fine cellular membrane, and at fhort, 

 but equal and regular, diftances a circle of fpine-like precedes iffue internally, 

 over which the cellular membrane is fpread, fo as to clofe up the tube tranf- 

 verfely at every diffepiment. 



Hydrodictyon. — Fila fub m mbranacea, tubulofa, ad angulos varies in 



.utrieulum retiformtm finibus fuis combinata, demum utriculum matri fmi- 



lem invagination produeentia. 



C. reticulata differs fo entirely from every other known Conferva?, that Dr. 



Roth has very properly formed it into a feparate genus, with the prefent ex- 



preflive name. The effential character in the fecond Fafciculus of his CatalecTi 



is takenwholly from the lingular contexture of its filaments, but this he has 



been enabled to amend in the third, by M. Vaucher's important difcovery of its 



ft ill more lingular propagation. 



Ulva. — Mtmbrana 'ex'anja, diaphana, fruiiificatienum granulrs praprhnts 



circa marginal! innatis. 



The genus, as here conftituted, is intended to comprehend only thofe fpecies 



which are compofed of a (ingle leaf-like membrane, the tubular ones having, 



as before mentioned, been removed to the Conferva, and U. incraffata, U; 



rukens, and their affinities, to the following family. 



Rivularia. — Sitbftantia gelatinofo-cartil.igi/iea, hyalina, integumento inem- 

 branacco defiituta; fr unification? s in flis geniculars intra fubflantiam 

 nidulantibus. 

 1 he plants which Dr. Roth has referred to this genus, are fo clofely allied 



