290 
displays so little of their real contour, that it will be found 
necessary to reconstruct and redescribe several of the existing 
genera, and amongst them the genus to which I am about to 
direct attention. 
Surirella, Turpin , 1827. 
Frustules, free, solitary, with equal extremities or cuneate. 
Valve with a median longitudinal clear line or space : pro- 
duced laterally into carinated alee, and folded transversely 
or obliquely into plicee alternately elevated and depressed : 
most strongly developed near the margins, and growing 
fainter towards the median line or space ; sides of the valve 
flexed inwards from the carinse towards the margin. 
Such I conceive to be the generic characters of Surirella, 
which have hitherto escaped recognition, owing, doubtless, 
to the imperfect observation afforded by the monocular 
microscope. 
This genus was first established by Turpin in 1827. 
Dujardin 1 says of his definition, which I have not seen, “ M. 
Turpin voluit faire un genre particulier de celles dont la forme 
est ovale, presque l’onde, et qui sont fortement ciselees; il 
les nomma Surirella.” In 1841 it was restricted by the 
formation of the genus Campylodiscus by Ehrenberg ; and 
still further in 1853 by the late Professor Smith in the con- 
struction of the genera Cymatopleura and Tryblionella. But 
the characters of Surirella, as given by Professor Smith, are 
by no means exact nor explanatory of the structure of the 
valve in this genus ; he describes the margins of the valve as 
“ produced into alse ;” 1 2 3 and in defining the genus Tryblionella 
he says “ it agrees with Surirella in the presence of alse, 
but these arise from the disc and are not, as in Surirella, 
prolongations of the margin .” s This description and the 
figures of the marginal views (F. V.) given in Plate viii, vol. 
i, show that Pi'ofessor Smith was not aware of the real 
structure of the frustule and conformation of the valve. The 
alee are not prolongations of the margin, nor placed at the 
margin, but are produced by the abrupt inflection or folding 
inwards of the sides of the valve, at a more or less acute 
angle, some distance from the margin; the point of flexure 
forming a carina on either side. Thus the valve has three 
1 ‘ Hist. Nat,, des Infus.,’ p. 673. 1841. 
3 * Synop. of Brit. Diatom./ vol. i, p. 30. 
3 Op. cit., p. 35. 
