468 DESCEiPTioN OF [ VolygastHca, 



arc very doubtful members of this genus, and, more probably, apper- 

 tain to Sphenella ; tlieii' pedicle (stipes) not having been seen. 



The following species and remarks are taken from some valuable 

 papers of Mr. Ealfs (Ann. Nat. Hist. vol. xii. p. 460.) 



GojirnoNEMA geminatum (Agardli.) — Densely tufted, frustules 

 narrow, cuneate, the puncta at the upper end wanting, or nearly so ; 

 lateral surfaces urn-shaped, striated. Found on rocks in sub-alpine 

 streams. 



The plant forms tufts of a spong)^ texture, not at all mucous, 

 composed of the densely woven filaments. In a young state its 

 colour is brownish, from the frastules covering the surface, but as 

 these fall off it becomes whitish, and indeed not unlike a tuft of 

 wool. Filaments are repeatedly dichotomous, frustules of large size, 

 simple or binate. There is a central, longitudinal, pellucid line, 

 slightly dilated at each end, with a larger dilation at the centre, 

 Avhich may be taken for a perforation, which, undoubtedly, it is not. 

 From this central punctum the striae are somewhat radiant. 



G. foUicBforme (Kvitz.) = G. truncatum (Ehr.) — Frustules with 

 two evident puncta at upper ends ; laterally, urn-shaped. A very 

 minute species which, to the naked eye, seems only a brownish dis- 

 colouration of the plant on which it grows. In the more perfect 

 form it resembles G. capitatum, as figured by Ehrcnberg, nor is there 

 any character in his description to distinguish the latter from this 

 s^jccies. 



In his last work, Kiitzing has described this species imder the 

 name of Gomplwnema contractum. 



Mr. Ralfs again says, " Ehrenberg appears to have confounded 

 this plant with G. geminatum (Agardh), which species, as well as 

 G. ^Jo/<?/<?/orjwe (Kiitz.) {i. e., the immature plant), he appends as 

 sjmonymous to his G. truncatum. If he had seen the true G. gemi- 

 natum, he could not have fallen into this mistake, for, besides the 

 immense difference between these plants in size and habit, their 

 frustules present sufficient marks of distinction. In G. geminatum 

 the front view is very narrow, sometimes nearly linear; in this 

 species the frustules are distinctly cuneate, and, notwithstanduig 

 their much smaller size, have two evident notches at the upper end, 

 wliich arc wanting in G. geminatum. The latenJ surfaces, too, JU'e 



