382 MR. G. S. WEST ON 
and regular curvature, and there is no trace of a ventral inflation ; 
whereas the average N.-American specimens, besides being of 
larger dimensions, have a distinet small inflation on the ventral 
surface and proportionately narrower ends. The following 
dimensions are those of a specimen from Nova Scotia for com- 
parison with those of the English specimens tabulated on 
p. 380:— Long. 380 u; lat. 53 p: lat. apic. 14 ju. 
3. CLOSTERIUM KUETZINGIT, Bréb., in Mém. Soc. Sci. Nat. 
Cherbourg, vol. iv. 1856, p. 156, t. 2. f. 40.—This is a species 
which retains a comparatively constant outward form, but ex- 
hibits considerable variation in the extent of the ventral inflation 
of the semicells and in the striolations of the cell-wall. 
The annexed table is a comparison of the measurements, &e., 
of several specimens taken from various parts of the country. 
The striations on those from Oxfordshire were not only fewer in 
number, but relatively stronger than those present on the 
majority of individuals from other localities, and for this reason 
the Oxfordshire examples might properly be relegated to var. 
vittatum, Nordst. (* Algol. Smäsak.,” Bot. Notiser, 1887, p. 163). 
| "NEN 
| Breadth ` Striolations 
| Specimens from Length. | Breadth, length. | in 104. 
| 
Westmoreland ......... 410p | 215p | 1:19:07 | 9 
W. Yorkshire ......... 426p | 239p 1:185 | 7 
Oxfordshire ............ 430 | Lin 1:307 | 5 
N. Wales ............... 434 u | 17 u 1:255 | 11 
4. EvasrnuM DIDELTA, Ralfs, in Ann. § Mag. Nat. Hist. 
vol. xiv. 1844, p. 190, t. 7. f. 2.— This species, which, in temperate 
regions, is one of the most widely distributed of the genus, was 
first described as Cosmarium Didelta by Meneghini, “ Synops. 
Desm.,” Linnea, 1840, p. 219, the name Heterocarpella Didelta 
having been given by Turpin (in Mém. du Mus. d' Hist. Nat. Paris, 
1828, tom. xvi. p. 315, t. 13. f. 16) to a plant of doubtful 
identity. Many forms of the species have been described, among 
whieh the following may be mentioned :—var. sinuatum, F. Gay, 
“Essai Monogr. Conj.,” Montpellier, 1884, p. 56, t. 1. f. 11; 
