DesmidiecB.'] infusorial animalcules. 273 



Penitjm: digitus = Cloderium digitus, and Polysolenia Closteriiim. 

 (Ehr.) — Smooth, elliptic-oblong, with rounded ends; fillets obscure, 

 undulated, inteiTupted only by a transverse band at the suture. 

 Terminal globules wanting, or very indistinct. Length 1-8 1st. 

 Three to five times longer than broad. 



P. internqyttnn. — Smooth, cylindi-ical ; extremities conical, -^^th 

 rounded apices; fillets three to foiu- strongly marked, interrupted by 

 three transverse bands. Ends colourless ; each occupied by a large 

 globule containing moving granules, as in Closteriiim. Length 1-11 6th. 

 Foui' to six times longer than broad. 



P. closteroides. — Smooth, fusiform or lanceolate ; longitudinal fillets 

 and terminal globules distinct. Ends obtuse ; vesicles in a single 

 longitudinal row. Length l-92nd. Six to ten times longer than 

 broad. 



P. truncatum. — ^^Veiy minute, smooth, cylindrical, with truncate 

 ends ; sporangia orbicular, easily detached from the conjugated 

 fronds. Two to three times longer than broad. Has a transverse 

 pale band, but, when empty, exhibits no suture. Length 1 -969th 

 to l-555th. 



P. Jenneri. — Smooth, cylindrical with rounded ends ; sporangium 

 orbicular, situated between the conjugating fr-onds, which are 

 deciduous. It agrees in size and form with P. Brelissonii, but differs 

 in the form of its sporangia. The conjugating fronds do not open 

 and gape at the sutui'e, as is usual in the Desmidiece, but couple by 

 small and distinct cylindrical tubes, like many of the Conjugatce. 

 Length 1-8 10th. Two to four times longer than broad. 



f t Sporangium permanenthj attached to the conjugated cells, at first 

 quadrate, then orbicular ( Cylindrocystis.) 



P. BrShissonii. — Smooth, cylindrical, with rounded ends ; sporan- 

 gium at first quadrate, but finally orbicular; conjugating fronds 

 persistent. Minute, often congregated into a mucus stratum on wet 

 mud. The transverse pale central band, which, in the Besmidiem, 

 indicates the line of junction of the segments, is less conspicuous 

 here than in any other species of the family. Length 1 -637th to 

 l-404th. 



Genus Docidium (Brebisson.) — Frond simple, straight, much elon- 



