ARCHER— ON A NEW SPECIES OF COSMARIUM AND PENICTM. 51 



General Description: — Frond very minute, about one-third longer than 

 broad, sub-elliptic, sides somewhat barrel-shaped, ends truncato-rotund ; 

 endrochome dense, a single large (amylaceous) granule in each half, 

 and showing two or three indistinct longitudinal "fillets," and an in- 

 distinct, pale central band; no moving granules at the extremities; 

 end-view, orbicular or very broadly elliptic ; empty cell- wall colour- 

 less, without markings. Zygospore in front- view quadrangular, oblong, 

 about 10:6 longer than broad, compressed, margins somewhat concave 

 at the centre, angles produced, mamillate, nipple-like at the extremi- 

 ties ; contents sparing, scattered ; in side view elongate, often with a 

 slight concavity at each side, ends rounded, extemities nipple-like ; in end 

 view, ovate, acuminate, extremities nipple-like. The empty parent-cell- 

 membranes persistent at each end of the zygospore. If, as is mostly 

 the case, the parent- cells conjugate in a parallel position, the zygospore 

 possesses a regular cushion-like figure, all its angles lying in the same 

 plane (PL I., Tig. 39). But, if during the conjugation, the parent- 

 cells lie at right angles to each other, there is then a corresponding 

 twist in the form of the zygospore, and in this case the angles at one 

 of its ends lie in a plane at right angles to those of the other. Appa- 

 rently from a similar cause, any intermediate degree of relationship in 

 this regard may thus take place. Misshapen or irregularly contorted 

 zygospores occasionally, but exceptionally, occur, in which one of the 

 corners may be inordinately drawn out, or the usual relative proportions 

 of length, breadth, and depth become partially or locally interfered 

 with. The mamillate form of the angles, and their nipple -like extre- 

 mities, are maintained, however, in all cases (Pigs. 39-44). The conju- 

 gating, as well as dividing, cells are surrounded by a distinctly bounded 

 gelatinous investment, which afterwards disappears. 



Measurements: — Length, y^j"' breadth, 20*00"; depth, ytjo'i °f an 

 inch. 



Length of zygospore, 7 ^ to ^ ; breadth, j^o- 



PL I., Pig. 34, frond with endochrome; 35, dividing frond; 36-38, 

 commencing conjugation; 39, front view of zygospore; 40, side view 

 of same ; 41, end view of same; 42-44, variously twisted zygospores. 



Affinities and Differences : — I do not doubt but that there might be 

 some, who, on looking at the mature unconjugated condition only of this 

 little plant, on account of its simple form and minute size, would be dis- 

 posed to regard it merely as an indescribable nonentity — perhaps a 

 dwindled or starved example of some other form — or, at best, as only a 

 transitional or gradational variety. It is true that, like many of its im- 

 mediate allies, it is only a minute, elliptic, or, as I have tried to describe 

 it, barrel-shaped cell ; nevertheless, the first moment I noticed it, even 

 in its unconjugated state, I thought not so, but felt that it was indeed 

 a new form, which I had never seen before. 



It is distinctly a species of Penium (Breb.), the structure of its 

 cell-contents removing it from Cylindrocystis (Menegh.) or Mesotsenium 

 (Nag.) — the entire want of a central constriction separating it from cer- 

 tain species of Cosmarium (Corda) — the same, as well as the want of a 



