258 Mr. J. Ralfs on the British Desmidiese. 



terminal notch, which is not seen in the lateral \aew. There is 

 also beyond the notch a remarkable lip-like projection which is 

 wanting in Tetmemorus Brebissonii, and the puncta seen in its 

 empty frond are not arranged in longitudinal rows. 



Plate VIII. fig. 2. Tetmemorus granulatus : a, front view; h, side view ; 

 c, empty frond ; d, fronds conjugated ; e, spore fully formed ; /, spore se- 

 parated from the segments; g, side view of conjugate fronds. 



P.S. — Since the preceding was written I have met with this 

 species in a conjugated state. The specimens were gathered near 

 Dolgelley, and formed a mucous stratum on the moist soil. 



The fi-onds were smaller than usual ; I did not observe any in 

 the first state of union, but it appears that after conjugation the 

 segments of the fronds are separated by the formation of a large, 

 quadi'ate, central cell, in which all the endochrome of both fronds 

 is collected and the empty segments remain loosely attached to 

 the corners of this cell. The endochrome at first fills the cell, 

 large starch globules being scattered throughout the minutely 

 granular substance, but at length it becomes a dense, round, ho- 

 mogeneous spore of a dark green colour which finally changes to 

 an olive-brown. In this stage the segments of the original fronds 

 fall off, leaving the quadrate cell inclosing the spore. 



In the front view, as stated above, the cell is nearly square, 

 the sides are concave, and the angles rounded and shghtly pro- 

 duced. A lateral view shows that the cell and spore are both 

 compressed. 



This is the first opportunity I have had of examining any of 

 this family in a conjugated state, and I have described it at some 

 length because it appears to me a very interesting and important 

 fact in support of then' claim to belong to the vegetable kingdom, 

 exhibiting in the present instance a striking similarity to the 

 change which takes place during the formation of similar spores 

 in Staurocarpus among the Conjugate. 



In StaurocarpiLS after conjugation a subquadrate cell is formed, 

 within which the endochrome is collected. The latter is at first 

 of the same form as the cell, but in one species at least is at 

 length condensed into a large, compact, globular spore, and in 

 every species the cell vAih. the contained spore finally separates 

 entu'ely from the filaments with which it is connected. In this 

 separate state I know no character by which to distinguish the 

 spore of the Tetmemorus from one belonging to a species of Stau- 

 rocarpus ; and in both, the spore, when tested by the tinctm-e of 

 iodine, is found to be almost wholly composed of starch*. 



* Examples of the shape of the cell in species of Staurocarpus may be 

 seen in the plate illustrating Mr. Hassall's valuable papers on the Fresh- 

 water AJgse. — Annals of Nat. Hist. vol. xii. pi. 7. 



