8 BRITISH PESMIDIACE^. 



number and in disposition, the commonest arrangements being 

 two (one vertically over the other), and four disposed in the 

 form of a cross. This variability was first pointed out by 

 Nordstedt. The side and vertical views of this variety also 

 differ to a certain extent from those of the type. 



Var. Taturnii var. nov. (PI. LV, fig. 4.) 



Cells with a widely-open, acuminate sinus, basal 

 angles of semicells subuncinate-mamillate ; polar lobe 

 aiivil-sliaped with a convex apex, incisions on each side 

 below the polar lobe widely excavated towards their 

 inner extremities ; cell-wall strongly punctate, with a 

 single large scrobiculation in the centre of each semi- 

 cell. Side and vertical views as in the type. 



Length 165/x,; breadth 110^; breadth of isthmus 



o ^ 

 O/ JJL. 



ENGLAND. Near Salisbury, Wilts! (E. J. Taturri). 



This variety occurred amongst numerous specimens of the 

 type in a collection from a Sphagnum-bog. 



The form of E. crassum described by Wood as " E. ornatum' 

 (ride Wood in 'Proc. Acad. Nat. Sci. Pliilad./ 1870, p. 17; 

 'Freshw. Alg. N. Amer./ 1873, p. 137, t. 21, f. 12), and sub- 

 sequently placed as " E. crassum var. ornatum ' ' by Hansgirg 

 (1888), may possibly be the same as this variety, but neither 

 the description nor the figure given by Wood is sufficiently 

 accurate to determine the identity of the form in question. 



Note. E. crassum var. corniibiense Benn. Alg. N. Cornwall, 

 1887, p. 16, t. 4, f. 19; Cooke, Brit. Desm., 1887, t. 65, f. 4 

 (from Bennett) ; De Toni, Syll. Alg., 1889, p. 1088. This 

 is a form of E. crassum with open interlobular incisions and 

 with the lateral protuberances on the margins of the lateral 

 lobes, which is most incorrectly described and still more 

 badly figured. " Protuberances" such as those described and 

 figured by Bennett do not occur on any known Euastrum. 

 Moreover, his dimensions are vastly different from the pro- 

 portions of his figure. 



3. Euastrum humerosum Ralfs. 

 (PI. XXXIV, figs. 1, 2.) 



Euastrum humerosum Ealfs, Brit. Desm. 1848, p. 82, t. 13, f. 2 ; Arch, in 

 Pritch. Infus. 1861, p. 729; Eabenh. Flor. Europ. Algar. Ill, 1868, 



