154 BRITISH DESMIDIE^. 



Very common, especially where water lodges in wet weather. Cornwall and 

 Wales, /. R. Ayrshire, Rev. B. Landshorough. Aberdeenshire and Banff- 

 shire, Br. Bickie and Mr. P. Grant. Northamptonshire, Rev. M. J. Berkeley. 

 Sussex, Kent, Surrey, and near Southampton, %Ir. Jenner. Ireland, Mr. An- 

 drews. Essex, Mr. Hassall. Near Bristol, Mr. Thwaites and Mr. Broome. 

 Westmoreland, Mr. Sidebothum. Rochdale, Mr. Coates. 



Falaise, Brebisson. Germany, Kiitzing. Princeton, New Jersey, with 

 sporangia, Bailey. 



Frond minute, often congregated into a mucous stratum on wet mud, in the 

 same manner as Tetmemorus gramdatus, its frequent companion, which at 

 first sight it resembles. The fronds vary much in size, from two to six times 

 longer than broad, and are oblong or cylindrical with rounded ends. The 

 transverse pale central band, which in the Desmidiese indicates the suture or 

 junction of the segments, is less conspicuous here than in any other plant of 

 the family. The endochrome being usually denser at the middle of each seg- 

 ment produces a resemblance to a joint of a species oiTyndaridea. The end 

 view is circular with a central nucleus. The empty frond is smooth and co- 

 lourless ; no suture can be detected in it. The sporangia have been gathered 

 by me at Dolgelley ; by Mr. Jenner on Piltdown Common and near Tunbridge 

 Wells, Sussex, and by Mr. Thwaites near Bristol. The process of conjugation 

 in this species differs from that in the rest of this genus ; for, as in Hyalotheca 

 dissiliens, the conjugating cells enter into the formation of the containing cell 

 and are permanently attached to the sporangium, instead of being at length 

 detached, as commonly happens in the Desmidiese. The sporangium is at first 

 cruciform, then quadrate, and finally orbicular, 



Penium Brebissonii has been placed with the Palmellese by Meneghini and 

 Brebisson, because the division into two segments is but obscurely indicated, 

 and its fronds often form a mucous stratum, I cannot however concur with 

 them, and I consider that it has been correctly removed by Kiitzing to this 

 family. Tetmemorus grunidatus, Cosmarium curtxim, and other undoubted 

 Desmidieae, form similar strata, are often mingled with it, and by the naked 

 eye cannot be distinguished from it. In its formation of sporangia this plant 

 also agrees with the undoubted members of the family. 



That this species has been referred to the Palmellese by such distinguished 

 algologists proves indeed how closely the families are allied. M. de Brebis- 

 son, in a recent letter, admits that it may belong to the Desmidiese, but con- 

 siders that the difference in the formation of its sporangia is a sufficient rea- 

 son for keeping the genus. Admitting that in strictness his view is correct, I 

 nevertheless place this species in Penium, because the conjugated state, occur- 

 ring so rarely, would seldom enable the student to distinguish between Penium 

 and Cylindrocystis. 



Length of frond from ^-|y to jij of an inch ; breadth from xtVf ^^ "sir '■> 

 length of side of quadrate sporangium from y^ to -g-^j- ; diameter of mature 

 sporangium -^-^. 



Tab. XXV, fig. 6. «, h. fronds with endochrome; r, d. empty fronds; 

 e, f, (J. imperfect sporangia ; h, i. mature sporangia. 



