88 THE JOURNAL OF BOTANY 



slightly greater than those of the typical form so frequent in the 

 rivers and lakes of Germany, but were not so great as the measure- 

 ments of var. lata Lemm. (Z. c. p. 30). 



12. Ehizosolenia morsa W. & G. S. West in Trans. Koy. Irish 

 Acad, xxxiii. sect. B, 1906, p. 109, t. 11, f. 5-7 ; G. S. West in 

 Journ. Linn. Soc. (Bot.) xxxix. 1909, p. 77, t. 3, f. 15-16 ; W. & 

 G. S. West in The Naturalist, 1909, p. 292, and fig. 2 on p. 187. 

 B. eriensis H. L. Smith var. morsa W. & G. S. West, 1905. This 

 species was found in association with Synedra actinastroides .in 

 tlie surface-waters of the canal at Lifford, in Worcestershire. It 

 is a characteristic constituent of the plankton of all the British 

 lake-areas, and its occurrence in the Midlands of England is both 

 noteworthy and interesting. Lat. valv. 4-8'5 /x. 



IV. — DiPLOCH^TE Collins and Polychj^tophora W. &G. S.West. 



The publication of a second species of Polychcetophora, namely. 

 P. simplex G. S. West,* has induced Collins f to place both 

 P. simplex and P. lamellosa j under his genus Diplochcete. He 

 states, with some reason, that if P. simplex is to be included 

 in the same genus as P. lamellosa, then both must be trans- 

 ferred to the genus DiplochcBte, of which a solitary species was 

 described in 1901. § It seems, however, impossible to regard 

 Diplochcete soUtaria and Polychcetophora lamellosa as species of 

 the same genus, and my own personal view is that for several 

 reasons they should remain as species of different genera. 



There now remains for discussion the systematic position of 

 Polychcetopliora siinplex. When I described this plant I had 

 grave doubts whether it should be placed in the genus Polychceto- 

 phora or a new genus created for its reception. The suggestion 

 made by Collins that it should be placed as a species of Diplochcete 

 seems to me almost a more erroneous view than its inclusion in 

 the genus Polychcetophora. The American '^l^n'i— Diplochcete 

 solitaria — possesses flattened cells with thick walls, each cell being 

 furnished with two bristles, usually at opposite poles, and arising 

 from the lower half of the cell. The figure given by Collins shows 

 these bristles to be rather short, stiff' and thick, and very different 

 in character from the slender, flexuose bristles of the British 

 plants. Moreover, Dipilochcete solitaria is a marine Alga epiphytic 

 on Laurencia ohtusa, a fact which must not be lost sight of. Few 

 genera of Algae are common to both fresh watei" and the sea, and 

 it is highly probable that these two plants, Diplochcete solitaria 

 and Polychcetophora simplex, have originated independently from 

 quite different sources among the lower green forms. Under these 



* G. S. West, " Some Critical Green Algffi," Journ. Linn. Soc. bot. xxxviii. 

 1908, p. 279, t. 20, f. 1-G. 



t F. S. Collins, "The Green Algae of N. America," Tufts College Studies, 

 Mass. vol. ii. no. 3, 1909, p. 278. 



\ W. & G. S. West, "Notes Alg. III.," Journ. Bot. March, 1903, t. 448, 

 f. 1-4. 



§ F. S. Collins, " The Algas of Jamaica," Proc. Araer. Acad, xxxvii. 1901, 

 p. 242. 



