ON GENERA AND SPECIES. ai 
sporangiferous receptacle, differences which, with two or = 
three exceptions, appear to me to be more useful as specific 
. than as generic characters; indeed, in some cases they are 
80 trifling that I have failed to find them. Under these 
circumstances I cannot see that any practical advantage 
. Will be gained by dividing Hymenophyllacee into so many 
. genera as Presl has done. 
» .. Hymenophyllacee also form the subject of a special mono- 
graph, published in 1858 by Dr. Van den Bosch, of Goes, 
Holland. It consists of seventy-nine pages octavo, and is 
entitled * Synopsis Hymenophyllacearum, Monographie ` 
. hujus ordinis Prodromus." It contains simply an enu- io 
meration of names of genera and species with references to ` 
. authors. He enumerates no less than 305 species, being Des S 
120 above that of Presl, and 156 above that enumerated ` S 
by Sir William Hooker in the “ Synopsis Filicum," here- 
. after to be noticed. The whole are arranged under nine 
genera, of which Hymenophyllum and Trichomanes alone ` 
. contain 254 species, The remaining fifty-one are divided — 
amongst seven genera, two of which contain a single 
Species each. He does not characterise any new genera, 
and only adopts five of Presl's. But his number of species ` — 
is so much in excess of that of other authors that, if he 
. really had specimens of the whole in his herbarium he 
. must have described his species on the different forms of ` ` 
fronds and other variable structure, which are always to 
be found in an extensive series of herbarium specimens, 
many such when carefully collated viti, a vage: 
species only. t 
l In 1849, Presl published another work, entitled a, Epimelia = 
Botanica,” or additions to and emendations of his * Tenta- — — 
en Pteridographew.” In this work he characterised no ; 
$ n miki tres new ege and described a consider. 
