38 BEIT1SH DESMIDIACE.E. 



immature cells intervene between the original adult semicells 

 (PL LXVIII, fig. 25). These immature cells are often set free 

 and commence division while still in a juvenile and unde- 

 veloped condition. The new semicells resulting from this 

 division are as often as not quite typical, showing all the 

 characters of the species (PL LXVIII, fig. 24). Thus, 

 if the distinctive features of a species are partially lost 

 through repeated rapid divisions, they may make their 

 appearance in a most pronounced manner in the semi-cells 

 of a succeeding generation. 



The most marked variety of this species var. productum 

 West and G. S. West ('Freshw. Alg. Ceylon/ 19U2, p. 166, 

 t. 20, f. 35) is known from Ceylon and Java. The superior 

 angles of the semicells are produced outwards to such an 

 extent as to appear almost like short processes. 



In 1903, Schmidt ('Grundl. Algenfl. Ltineburg. Heide/ 

 p. 21) placed this Desmid under the genus Spliserozosma, but 

 the plant which he had in such abundance in the filamentous 

 condition is without doubt a form of Sphserozosma Wallichii 

 Jacobsen. We have examined Cosmarium Regnesi from almost 

 every part of the world, and have described all its known 

 varieties. We have examined specimens from hundreds of 

 different collections, in some of which it occurred very 

 sparingly, in others in prodigious abundance, and we have 

 never yet seen what could be truly described as a filamentous 

 form of this species. The nearest approach to such a state is 

 the short chain of immature individuals resulting from very 

 rapid division, which we have figured on PL LXVIII, fig. 25. 

 Moreover, Schmidt has placed as synonyms of C. Regnesi 

 Desmids with which that species has not the slightest affinity, 

 his entire statements (I.e. pp. 21-23) appearing to us to indi- 

 cate a most superficial and imperfect knowledge of the plants 

 in question. 



Hansgirg has described a trigonal variety (var. trigonum) 

 of C. Regnesi from Bohemia. 



Var. tritum West, (PI. LXVIII, figs. 35, 36.) 



C. Regnesi var. tritum West, Alo-. W. Ireland, 1892, p. 149, t. 21, f. 3 ; 

 West & G. S. West, Alg. Madag. 1895, p. 59, t. 9, f. 24. 



Semicells with the angles bluntly rounded and not 

 toothed. 



Length 6'6-8'5 /i ; breadth fvG-8'5/*; breadth of 

 isthmus 3'7 5/x; thickness 3*9-4 i, 



