54 BRITISH DESMIDIAf'E/E. 



Mesotseni-um caldarioncni (Lagerh.) Hansg. Prodr. Algpnfl. Bohm. 1888, 

 p. 174; r'Tiirn. Freshw. Alg-. E. India, ISO:;, p. 15, t, 1, f. 23; West 

 & G. 8. West, Alga-fl. Yorks. 1900, p. 42. 



Cells cylindrical or subcylindrical, 2-|-4 times longer 

 than their diameter, somewhat suddenly attenuated near 

 the apices which are rounded; chloroplast axile, some- 

 times a little irregular and bent, often with one pyrem >i< I . 



Zygospore unknown. 



Length 27-46 ^u; breadth 10-5-11-5 /i. 



ENGLAND. Bradford, Yorkshire ! forming a gela- 

 tinous stratum in a greenhouse with M/r////W///rr 

 l!rtt/ri/ii Lagerh. 



Geoc/r. Distribution. Sweden. India? Ecuador. 



We have previously mentioned that Turner's figure docs 

 not represent the species. It is a most characteristic .Zl/f.W.r- 

 'ir'nim owing to the sudden attenuation of the extremities of tlie 

 cells; there is also an almost imperceptible narrowing of the 

 middle region of the cells. It must be a very rare plant as we 

 have only once obtained specimens of it. 



6. Mesotsenium truncation *y/. nov. 

 (PL V, fig. 12.) 



Cells cylindrical, 3-3-| times longer than their dia- 

 meter, apices broadly truncate;, chloroplast axile, 

 narrow, generally with a slight notch in the middle 

 region of the cell, with two pyrenoids. 



Zygospore unknown. 



Length 31-35 A < ; breadth 9-5-10/1. 



ENGLAND. Cowgill Wold Moss, Widdale Fell, West 

 Yorkshire ! 



This plant is readily distinguished from all other species of 

 this genus by its broadly truncate apices. It resembles Penium 

 trnncatum Breb. in its general outline but is at once dis- 

 tinguished by its plate-like chloroplast. 



A few individuals were observed in which there were two 

 plate-like chloroplasts, one in each half-cell. Sometimes one 

 chloroplast was disposed in a plane at right angles to the 

 other, so that the flat surface of one was seen concurrently 

 with the edge of the other. 



It was found amongst mosses on wet rocks. 



