GENICULAEIA. 37 



Length 300-427 /u ; breadth 14-16'3/u; breadth of 

 apices 17-18' 5 //. 



ScoTLAXJ). In the plankton of Loch nan Eun, N. 

 Uist, Outer Hebrides ! 



We have only observed this interesting species in the 

 plankton collections from the above-mentioned lake. It i> 

 distinguished from G-. spirotwuia De Bary by its narrower 

 and more elongated cells, and by the fewer turns and laxor 

 disposition of the two spiral chloroplasts. 



Tribe 2. SPIEOT^NIEJ:. 



In the genera of this tribe (with the one exception 

 of Aui-i/lni/ci/m, which is not a British genus) the cells 

 are solitary, relatively short, and unconstricted (with 

 the exception of a few species of Cylindrocystis). The 

 cell-wall is not differentiated into two layers and is 

 quite smooth. The individuals do not reach maturity 

 by the mere growth of the younger half-cell, but there 

 is a subsequent periodical growth, chiefly in length. 



Genus 3. SPIROT^ENIA Breb. 1848. 



Breb. in Ealfs' Brit. Desui. 1848, p. ITS. 

 Arch, in Pritch. Iiifxis. 1861, pp. 720 and 751. 

 Cooke, Brit. Desm. 1886, p. 50. 

 De Toni, Syll. Algar. 1889, p. 807. 

 Liitkem. Gatt. Spirotaen. 1895, p. 92. 



Cells straight or almost straight, oblong-cylindrical 

 or fusiform, not constricted, apices rounded, subacutr. 

 or acute; with a single chloroplast, band-like and 

 parietal, or axile and cristate (or ridged), spirally 

 twisted to the left; nucleus excentric ; cell- wall 

 smooth and colourless. 



Species of this genus are never abundant and are mostly 

 very uncommon. They are met with sparingly either 

 amongst other Desmicls in collections from bogs, or occa- 

 sionally from wet rocks. They are easily overlooked owing 

 to the delicate nature of the cell-wall and their generally 

 inconspicuous appearance. There is frequently great diffi- 

 culty in determining the precise nature of the chloropiast, 



