44 



THE GENUS TETRAPEDIA (REINSCH) WITH TWO 

 NEW FORMS. (Plate iii.) 



By William Archer. 



Amongst unicellular Algse falling under the class Chlorophyl- 

 laceae, forms with specially figured cells — that is, otherwise than 

 globular, ellipsoidal, or cylindrical, with more or less abruptly or 

 broadly rounded ends — are, as is well known, numerous ; but 

 amongst such plants belonging to the class Phycochromaceae, so 

 frequently found in the same situations associated with the fore- 

 going, so far as I am aware, not until recently has attention been 

 drawn to any examples of a specially figured outline. 



It does not appear, until the genus Tetrapedia was founded by 

 Professor Reinsch* for two new and singular exceedingly minute 

 chroococcaceous forms, that examples of specially figured forms 

 were known in this family of AlgEe. Inasmuch as Reinsch 's work 

 is but little known in this country, and as I have on one occasion 

 encountered his T. Crux-Michaeli'va this country, and am acquainted 

 with two other forms of a kindred nature, it has appeared to me that 

 a brief notice thereof might find a fitting place in these pages, ac- 

 companied by a reproduction of Reinsch's plate, and a sketch of 

 my own forms, reserving a fuller description and details to be pub- 

 lished elsewhere, in deference to the limited space which can be 

 devoted to this subject in this Journal. 



The description given by Reinsch of his genus is as follows : — 

 Class. Phycochromaceaa. 

 Family. Chroococcacese. 

 Genus. Tetrapedia, Reinsch. 

 Cellulae solitariaB aut farms consociatione individuorum plurium 

 familias ex cellulis binis, quaternis aut 16is exstitutas constituentes, 

 in sciagraphia quadratics, cellula singula incisuris quaternis in 

 cellulas filias quaternas dilapsa, cellula? filite post divisionem indi- 

 viduas singulas se prgebentes, incisurarum directio in marginum 

 lateralium directione perpendiculari aut in angulo semirectangulo 

 versa ; cellularum interanea granulosa, colore aerugineo. 



So far as our acquaintance with these little Alga3 reaches there 

 appear to exist four (if not five) distinct, yet kindred forms of 

 figured " Chroococcacese " — their remarkable shapes preclude their 

 being regarded as " Lichen-gonidia," but whether mature plants 

 or stages in the growth of any more complicated structure remains 

 a problem. Ours are at least forms which here and there recur, 

 and one can at once recognise them as always offering the same 

 characteristics and as maintaining their apparent individuality. 

 Whether they are " species " or not, it may be a matter of conve- 

 nience, should observers meet them elsewhere, and be able to throw 

 a light upon them, to have at least a means of their recognition ; 

 for these reasons it occurs to me as desirable (at least, provi- 



* " Die Algenflora des mittleren Theiles von Franken," by Prof. Paul Keinsch. 

 Etirnberg, 1867, p. 37, t. ii. f. 2, and t. i. f. 6. 



