48 BRITISH DESMIDIACEJE. 



Ursinella cruciata Kuntze, Revis. gen. plant. 1891, p. 924. 

 Cells small, about as long as broad, deeply constricted, sinus 

 narrow, widening outwards ; semicells truncate-pyramid ate, 

 inferior angles broadly rounded, apices broadly truncate, 

 margin slightly crenate. Vertical view elliptic, with a small 

 submamillate protuberance at the middle on each side. Side 

 view subcircular, with a small protuberance on each side. 

 Cell-wall finely granulate. Chloroplasts axile, with two 

 pyrenoids in each cell. 



The above description is based upon the indifferent figures 

 of Brebisson and of Wolle. Messrs. Eoy and Bissett have 

 recorded C. cruciatum from Scotland as "Not common. Alford, 

 Aberdeen ; Cammie, Cowie, etc., Kincardine/' We are in- 

 clined to regard Brebissoir's figure as belonging to some form 

 of C.punctulatum, a variety of which (var. Itrafdliense Nordst.) 

 possesses two pyrenoids in each semicell. Nordstedt (in litt., 

 July, 1907) writes "I have never seen any Desmid which I 

 could identify with the figure of C. cruciatum Breb." 



COSMAEIUM TCRPINII Breb. var. CAMBRICUM Joshua, New and 

 Rare Desm. 1885, p. 35, t. 254, f. 8. Joshua's figure is a very 

 poor one, but we believe this Desmid to be most probably 

 identical with C. didymoprotupsum W. & G. S. West (Consult 

 Vol. Ill, p. 192. t, 88, f. 8). 



Genus 16. XANTHIDIUM Ehrenb. 1837. 



Ehrenb. in Abh. Berlin. Akad. 1837 [1836], p. 114; Infus. 1838, p. 146. 



Menegh. Synops. Desm. 1840, p. 223. 



Kiitz. Phyc. g-ener. 1843, p. 162. 



Hass. Brit. Freshw. Alg. 1845, p. 358. 



Ealfs, Brit. Desm. 1848, p. 111. 



Kiitz. Spec. Algar. 1849, p. 177. 



Arch, in Pritch. Infus. 1861, pp. 720, 735. 



Eabenh. Flor. Europ. Alg. Ill, 1868, p. 221. 



Lund. Desm. Suec. 1871, p. 74. 



Kirchn. Alg-. Schles. 1878, p. 154. 



Wolle, Desm. U. S. 1884, p. 92. 



Cooke, Brit. Desm. 1887, p. 129. 



Holdt, Desmid. Gronland, 1888, p. 31. 



De Toni, Syll. Alg. 1889, pp. 905, 916. 



Turner, Freshw. Alg. E. India, 1893, p. 103. 



G. S. West, Treatise Brit, Freshw. Alg. 1904, p. 168. 



Wille in Engler & Prantl, Naturlich Pflanzenfam. 1909, p. 9. 



Holacanthum (Lund.) Wille in Engler & Prantl, Natiirlich Pflanzenfam. 



1890,1,2, pp. 7, 11. [ = Subgen. Holacanthum Lund. Desm. Suec. 1871, 



p. 75]. 

 Schizacanthum (Lund) Wille, 1. c. p. 11 [ = Subgen. Schizacanthum Lund, 



1871]. 



