82 BRITISH DESMIDIACE^. 



Creggan, Molier, and Shannacloontippen, G-alway ! 

 Adrigole, Kerry ! 



Geogr. Distribution. France. Germany. Austria. 

 Norway. Sweden. Denmark. Bornholm. Finland. 

 Poland. Faeroes. India. Ceylon. Madagascar (var.). 

 Central Africa (var.). United States. West Indies. 

 Brazil. 



We do not understand how any one could confuse this 

 pretty little species with Micrasterias oscitans Ralfs, to which 

 it bears only a superficial resemblance. It is one of the most 

 distinctive species of the genus, and notwithstanding its wide 

 geographical distribution it maintains its features very 

 constantly. 



Monstrosities of this species are sometimes found, such 

 as those figured by Elfving (' Anteck Fin ska Desm/ 1881, 

 t. 1, f. 1) and mentioned by Koy as sometimes occurring in 

 Scotland (vide Roy & Biss. ' Scott. Desm/ 1893, p. 174). 



One form from Ireland is worthy of special mention. We 

 have given a figure of it on Plate XLI (fig. 12). It possesses 

 an additional tooth above the bifid lateral angles, and was 

 observed in quantity from Ballyiiahmch, Gralway. The same 

 form is known from the United States (vide West and Gr. S. 

 West, ' Some Desm. U. S/ 1898, p. 295). 



A number of varieties of this species occur in America 

 which have not yet been found in Europe. One of these 

 var. trigona West which is known from Maine, is particularly 

 interesting, as it was the first triquetral specimen of a 

 Micrasterias to be described. 



3. Micrasterias truncata (Corda) Breb. 

 (PI. XLII, figs. 1-8 ; PL XLV, figs. 5, 6.) 



? Euastrum Rota Ehrenb. Entwick. Lebends. d. Infus. 1832, p. 82 [for 



all practical purposes only a name] ; Infus. 1838, p. 161, t. 12, f. 1 



[in part ; 1 g and 1 h = M . truncata]. 

 Cosmarium truncatum Corda in Aim. de Carlsbad, 1834, p. 180, 206, t. 2, 



f . 23, 24. 

 Cosmarium quadragies-cuspidatum Corda in Aim. de Carlsbad, 1840, 



p. 215, t. 6, f. 40. 

 Micrasterias truncata (Corda) Breb. in E-alfs' Brit. Desm. 1848, p. 75, t. 8, 



f. 4, t. 10, f . 5 ; Arch, in Pritch. Infus. 1861, p. 727 ; Eabenh. Flor. 



Europ. Alg. Ill, 1868, p. 199 (c. fig. 626), 191; Delp. Desm. Subalp. 



1873, p. 89, t. 5, f . 6-10 ; Jacobs. Desm. Danem. 1875, p. 152, t. 8, f . 2-8 



(formse monstrosse) ; Kirchn. Alg. Scliles. 1878, p. 162 ; Wolle, Desm. 



U. S. 1884, p. 114, t. 38, f. 6 ; Cooke, Brit. Desm. 1886, p. 60, t. 25, f. 2 ; 



De Toni, Syll. Alg. 1889, p. 1115; West, Alg. N. Wales, 1890, p. 287; 



