Desmidiece.'] infusoeial animalcules. 23ft 



same apparent breadth, and consequently, in all these respects, differs 

 from Did/ymoprium. 



Hyaxotheca dissiliens = Conferva dissiliens, (Smith.) — Filament 

 fragile, crenate; a shallow groove round each joint, dividing the en- 

 dochrome into two portions. The ti'ansverse view is circular, and 

 shows a mucous border of the same form. In this aspect too, the 

 endochrome is generally disposed in a stellate manner, with six or 

 seven rays, and frequently has a colourless central spot. This plant is 

 very fragile, breaking into single joints, each MT.th a perfect mucous 

 covering. Conjugation takes place by tubes : sporangia, cii-cular. 

 (P. 13. f. 32. 35. ; f. 32 a ti-ansverse view.) 



H. mucosa (Ehr.) — Filament scarcely fragile ; joints not constricted, 

 but having at one of the ends a minute bidentate projection on each 

 margin, the adjoining end of the next joint being similar. The 

 filaments have a very broad mucous sheath. The joints seem to be 

 in pairs ; a single one is consequently asymmetrical. 



H. dubia. (Kiitzing.) — Filament without a mucous tube ; joints 

 rather broader than long, with two puncta near each margin. 



H. cylindrica. (Ehr.) = Besmidmm cylindricum, (Greville and 

 de Brebisson, 1835.) See Did/ymoprium Grevillii. 



Genus Didymopeium. — Filaments elongated, gelatinous, fragile, 

 regularly twisted cylindrical, with a bidentate process or angle on 

 each side of the joints ; hence the margins of the filament are crenate. 

 The twisting of the filament causes it to appear of unequal breadth, 

 and the form of its joints to vary according as more or less of the 

 angles is seen at the margin. In a transverse view the joints are 

 cfrcular or broadly elKptic, with two minute opposite projections, 

 formed by the angles. The endochrome is radiate ; its rays from 

 foui' to seven. (P. 13. f. 38.) 



Bidymoprium differs from Desmidhim in having only two angles. 

 In a transverse view, the latter presents a cell truly angular, irre- 

 spective of the bidentate projections, and an endochrome divided into 

 a number of rays corresponding with the number of angles ; neither 

 of these circumstances occur in Didymoprium. 



The filaments of this genus increase in length, by the repeated 

 division of the joints, exactly as in the other genera, the new portions 



