148 BRITISH DESMTDIACEyE. 



become somewhat irregular in outline owing to rapidity of 

 cell-division. The striations on the cell-wall are exceedingly 

 fine and delicate, and as a rule can only be observed on old 

 individuals in which the cell-wall has become tinted. 



The cells are often rather suddenly attenuated near their 

 apices, and the extreme apex is commonly truncate and 

 sometimes slightly thickened. This character,, which is 

 undoubtedly very variable, was first mentioned by Clntwinski, 

 who gave the name of "var. trunc-atum" to those forms which 

 possessed it. 



Cl. acerosum is found most abundantly in low-lying districts, 

 and for this reason there are large areas of Scotland in which 

 it is very rarely observed. 



Var. elongatum Breb. (PI. XVIII, fig. 1.) 



CL acerosum 13 Ralfs, Brit. Desm. 1848, p. 164, t. 27, f. 2 c. 

 Cl. acerosum var. elongatum Breb. Liste Desm. 1850, p. 152. 

 CL acerosum var. acerosum Cooke, Brit. Desm. 1886, p. 21. 



Cells larger than in the typical form, relatively a 

 little longer, and with the striolations of the cell-wall 

 more distinct ; cell-wall of a yellowish-brown colour. 



Length 525-790 p ; breadth 29-50 p.. 



ENGLAND. Near Bristol, Gloucestershire (Thwaites). 

 Sheep's Green, Cambridge ! 



Geoyr. Distribution. France. Germany. Ceylon. 

 Mexico. 



Var. minus Hantzsch. 



Cl. acerosum var. minus Hantzsch. in Babenh. Alg. Eur. 1861, no. 1047 ; 



Hansg. Prodr. Algenfl. Bohm. 1888, p. 179 ; De Torn, Syll. Als?. 1889, 



p. 825. 

 Cl. angustum Hantzsch. in Rabenh. Alg. 1861, no. 1206; Rabenli. Flor. 



Em-op. Al-ar. Ill, 1868, p. 132 ; De Toni, Syll. Alg-. 1889, p. M9. 

 Cl. acerosum B. medium Reinsch, Algenfl. Frank. 1867, p. 1N6. 

 Cl. acerosum E. angustum Reinsch, I.e. p. 187. 

 Arthrodia angusta Kuntze, Revis. gen. plant. 1891, p. 883. 



A little smaller than the typical form, with a smooth 

 and colourless cell- wall. 



Length 176-330 /A; breadth 20-27 /A. 



ENGLAND. Leicester ( Roif) . 



SCOTLAND. Near Slains Castle, Bonrtie, Little Don 

 at Hanghton, Aberdeen (Roy $ 7//x.sv<//). Plankton of 

 Loch Fadaghoda, Lewis, Outer Hebrides ! 



Geoyr. Distribution. Austria. Ecuador. 



