68 BRITISH DESMIDIACEJK. 



rounded (very slightly subrectangular), superior part 

 of lateral margins retuse, apex somewhat protracted, 

 convex-truncate and retuse-emarginate in the middle, 

 superior angles rounded. Side view of semicell ovate- 

 truncate. Vertical view elliptic, poles slightly angular, 

 with a very slight inflation at the middle on each side. 

 Cell-wall finely granulate, granules much reduced in 

 the centre of the semicells, and quite absent at and 

 just below the apical emargination, often with an arc 

 of larger granules in the middle of the semicells about 



o o 



two-thirds the length from the base. 



Zygospore unknown. 



Length 85-89 p, (rarely only 65 p.) ; breadth 71-72 p, 

 (rarely only 60 fi) ; breadth of apex 33-3 7 ^ (rarely 

 only 27 ft) ; breadth of isthmus 20 p. ; thickness 36-42 p.. 



WALES.- -Llyn Coron, Anglesey ! 



Geogr. Distribution. Canada. United States. 



We have only once observed this Euastrum from the 

 British Islands, but have examined numerous specimens from 

 Nova Scotia, Maine, and Massachusetts. Fig. 20, PL XXXIX, 

 is the first accurate figure of this Desmicl published, and so 

 that there should be no doubt as to its identity the drai'-'nuj 

 w.y made from one of Joshua's original specimen*. 



Borge (' Alg. erst. Regnell. Expecl./ II, Desmid. 1903, p. 

 99) suggests a relationship between E. occidentals and Cosma- 

 rium Turpinii Breb., but the latter is considerably smaller, 

 with two small central protuberances, and without an emargi- 

 iiate apex. We know C. Turpinii very well, as it is frequent 

 in some parts of the British Islands, and it never has such a 

 protracted apex as E. occidentals. 



E. Occident ale has very little in common with E. verr-ucosum. 

 For the reasons for adopting the specific name "occidentale ; 

 consult West & G. S. West, ' Some Desm. U.S.' 1898, p. 293. 



40. Euastrum insular e (Wittr.) Roy. 

 (PI. XL, figs. 11-13.) 



Euastrum binale (Turp.) Ehrenb. var. insulare Wittr. Gotl. Ol, s<">tv. 



Alg. 1872, p. 49, t. 4, f. 7; Arch, in Quart. Journ. Micr. Sci. 1873, 



p. 434 ; Cooke, Brit. Desm. 1886, p. 76, t. 35, f. 10 ; De Toni, Syll. Alg. 



1889, p. 10S5 ; West, Alg. W. Ireland, 1892, p. 140 ; Johns. Bare Desm. 



U. S. 1894, p. 286, t. 211, f. 8. 

 E. insulare (Wittr.) Koy in Scott. Naturalist, April 1877 ; July, 1883 ; 



Eoy & Biss. Scott. Desm. 1893, p. 177 ; West & G. S. West, Alg. S. 



