152 BRITISH DESMIDIEiE. 



Besides the central transverse band present in all the Desmidiese, Penium inter- 

 ruptum has two others ; the fillets and endochrome are consequently divided 

 into four portions. The ends are colourless, and each is partly occupied by a 

 large globule, which contains moving granules like those in Closterium. The 

 empty frond is colourless vdthout markings, and there is no transverse line at 

 the middle. 



In a recent state this is a remarkable plant. The fillets are more strongly 

 marked than in any other species I have met with, and the checkered appear- 

 ance produced by the transverse bands essentially distinguish it. It must 

 however be observed that this character is lost in the dried state, when its 

 straight, cylindrical fronds have some similarity to those of Penium Digitus ; 

 but they are longer in proportion, their sides more parallel, and their extre- 

 mities more conical. 



Length of frond y^ of an inch ; breadth -g-yr* 



Tab. XXV. fig. 4. a. frond magnified 400 times ; b. frond magnified 200 

 times. 



5. P. closterioides ; frond smooth, lusiform or lanceolate; lon- 

 gitudinal fillets and terminal globules distinct. 



Penzance and Dolgelley, /. R. Ashdown Forest, and Piltdown, Sussex ; 

 Reigate, Surrey ; and near Southampton, Mr. Jenner. 



Frond six to ten times longer than broad, straight, lanceolate ; end obtuse ; 

 fillets and terminal globules distinct ; vesicles in a single longitudinal series. 

 Empty frond colourless and without markings. 



Penium closterioides in its appearance and in the arrangement of its endo- 

 chrome agrees better with Closterium than with Penium, and strongly resem- 

 bles the side view of some species of the former. The frond however is 

 always straight, and the opposite margins are symmetrical. 



Length of frond ~ of an inch ; breadth -g-g~o . 



Tab. XXXIV. fig. 4. a. frond with endochrome; b. empty frond. 



6. P. tnuicatum (Breb.) ; frond smooth, cylindrical with truncate 

 ends; sporangia orbicular, easily detached from the conjugated 

 fronds. 



Cylindrocystis truncata, Brebisson, in lit. cum icone (1847). 

 Dolgelley, J. R. 

 Falaise, Brebisson. 



Frond very minute, two or three times longer than broad, smooth, cylin- 

 drical with trinicate ends, sometimes slightly constricted at the middle. The 

 endochrome is similar to that of Penium Brebisson ii, but the transverse pale 

 band at the middle is usually more distinct. 



The empty frond is colourless, and its suture imperce})til)le. I believe that 

 it is minutely dotted, but the dots are too indistinct to assist in defining the 

 species. 



I have gathered the sporangia rather abundantly in a pool near Dolgelley ; 



