58 BRITISH DESMIDIE.E. 



On account of the oval form of the jomts their respective angles are sepa- 

 rated, and thus the filament acquires a pinnatifid appearance. 



The transverse view is broadly elliptic, with a small process at each end, 

 representing the angles. The mucous sheath is of the same form, and protu- 

 berant over the processes. The endoehrome is four- or five-rayed. 



I have gathered the conjugated state of Didymoprium Grevillii near Dol- 

 gelley. It has been found in France by M. de Brebisson, but I believe that 

 the present is the first description of it. 



Before coupling D. GreviUii separates into single joints (in only one instance 

 have I observed two joints of one filament still united and conjugated with 

 two other separated joints) ; the cells gape at the margins opposed to each 

 other, exactly as described under Hyalotheca dissiliens, but to a smaller 

 extent, and the original joint is far more easily detected, as one of the teeth 

 of the angle bounds the cleft ou each side. As the cleft is narrower, there is 

 an absence of the notch-like appearance so evident on the outer margin of 

 Hyalotheca dissiliens. The cells become connected by a narrow process, 

 often remarkable for its length, and the contents of one cell passes through it 

 into the other, and a sporangium is formed in the same manner as in many ol 

 the Conjugatse, The transfer of the endoehrome takes place in a mass, and 

 one part may frequently be observed uniting vrith that in the receiving-cell 

 whilst the other is still in the tube. The joints couple in a crossed position, 

 as in Hyalotheca dissiliens, but the length of the connecting tube permits 

 them to remain apart. The joint which contains the sporangium is but little 

 altered in a transverse view, and when the empty cell becomes detached can 

 scarcely be distinguished, except by contrasting the denseness of the endo- 

 ehrome with its stellate appearance in the unconnected joints. This detach- 

 ment of the empty cell is a frequent occurrence after the process is completed, 

 nd forms another character of resemblance to those Conjugatse which bear 

 the sporangium within the cell. 



In a front view the sporangium is as orbicular as the quadrate form of the 

 joint will permit, being of course rather broader at the side which is cleft, and 

 on that side is usually sHghtly protuberant. The mucous covering remains 

 unaltered on the joints when they are coupled. 



Length of joint ^-^ of an inch ; breadth of filament including teeth -^ ; 

 breadth of filament when the teeth are hidden, from -^ to -^ ; breadth of 

 sheath from ^-i^ to -3^2-. Diameter of sporangium j^. 



Tab. II, a. portion of a filament ; b. dividing joint; c. separated joints ; 

 d. transverse view ; e, f, g. conjugated cells ; h, i, k. sporangia. 



2. D. Borreri (Ralfs) ; joints inflated, barrel-shaped, longer than 

 broad ; transverse view circular. 



Desmidium Borreri, Ralfs, Annals of Nat. Hist. v. 11. p. 375. t. 8. f. 4. 



(1843) ; Trans, of Bot. Society of Edinburgh, v. 2. p. 8. t. 2. Hassall, 



Brit. Freshwater Algce, p. 343. t. 83. f. 9. 

 Didymoprium Borreri, Ralfs, Annals of Nat. Hist. v. 10. p. 10 (1815); 



Trans, of Bot. Society of Edinburgh, v. 2. p. 164. .Tenner, Flora of 



Tunb ridge U'ells, p. 102. 



