for tJie Microscope. 23 



skeleton, and are not so easily or successfully mounted 

 and preserved. 



165. ROUND-THREAD DESMID (Hyalotheca dissiliens). 

 This species consists of an elongated jointed filament with 

 a transparent gelatinous envelope. Each joint is con- 

 stricted at its point of union with the next joint, and the 

 contents are divided transversely into two portions. 

 Common, and often plentiful. (PI. III., fig. i.) 



1 66. TRIANGULAR-THREAD DESMID (Dcsmidium Swart- 

 zii}. Also united in filaments, which are triangular, the 

 twisting of which causes a zigzag line down the filament. 

 Each joint is constricted at its junction with the next, and 

 notched in the middle, with two teeth to each segment 

 above and below the notch. The contents also divided 

 into two portions. Common both in England and Ame- 

 rica. (PL III., fig. 2.) 



167. LARGE STAR DESMID (Micrastcrias denticulatd). 

 Single, not connected in filaments. Circular, and 

 divided into two segments, each of which is five-lobed, 

 with the middle lobe the smallest; each of the larger 

 lobes is again notched. Common. (PI. III., fig. 3.) 



1 68. WHEEL DESMID (Micrasterias rotata). So much 

 like the last that it is easily confounded with it ; the chief 

 differences being that the margins of the divisions are 

 toothed, and the middle lobes of each segment have each 

 three notches instead of one. (PI. III., fig. 4.) 



169. SMALL STAR DESMID (Micrasterias truncatd). 

 This is very much smaller than either of the preceding, is 

 also circular, and divided into two segments, of which 

 each is five-lobed ; but the end or middle lobe is much 

 the broadest, the other lobes being sharply toothed. 

 Common. (PI. III., fig. 5.) 



170. OBLONG DESMID (Euastrnm oblongum}. This 

 desmid is of an oblong form, and smooth, divided at the 

 centre into two equal segments, which are five-lobed. The 

 notches between the lobes are broad, and the lobes have 

 the corners rounded. (PI. III., fig. 6.) 



171. THICK EUASTRUM (Euastrum crassum}. About 

 the same size as the last, but more four-sided, with the 



