olt Proceedings of the Royal Irish Academy. 
FAMILY VI. STRIATELLEA, Kiitz. 
Frustules precisely as in the immediately preceding family, and 
distinguished by the possession of internal diaphragms, which, spring- 
ing from the connecting membrane, are interposed between the two. 
opposite valves. 
This family, since it was constituted by Kiitzing, has been adopted 
by successive authors, but with some div ergence respecting the species 
comprehended within its limits. As here defined, it embraces not 
only the genera included in Kiitzing’s family Striatellea, but also 
those of the family Tabellaricz, which, though generically distinct, 
come properly within the same limits. The Genera Gephyria and 
Eupluria, which were included by Ralfs, are here excluded from the 
family ; because in whatever other respects they may agree, they stand 
remote in consequenee of the unsymmetrical structure of the opposite 
valves. And for a similar reason I exclude Podosphenia, which Hei- 
berg placed in the family, the frustules bemg unsymmetrical both on 
front and side view. 
Thus defined, the family is precisely equivalent to Grunow’s sub- 
group of Diatomez, and stands out distinguished by two very decided 
features, namely, the perfect symmetry of the valves, and the inter- 
position between them of diaphragms more or less numerous. 
The diaphragms constitute so important a feature in the family, 
that some observations are needed to explain their nature and mode of 
growth. As far as 1 know, Ralfs was the first who described these 
organs with any tolerable approach to accuracy. He says :—‘‘ The 
appearance of longitudinal strize is in fact produced by silicious plates, 
arising internally from the margins of the filament, and extend- 
ing towards, but not reaching, the centre. The interior is thus 
divided into chambers opening into a central space. When viewed 
laterally, this central space resembles a canal, especially as the inner 
edge of each plate has a concave outline.”’ Ralfs, in Pritch., p. 808. 
If there be anything vague in this description, it is greatly elucidated 
by the observations of Wm. Smith, as well as by the figures of these 
diaphragms in the case of Rhabdonema, Tetracyclus, and Tabellaria, 
B. D., Vol. i., pp. 82-34, Pl. xxxviii., fig. 306 h and 305}, Pl. xxxix., 
fig. 308 h and ier xliii., fig. 316} and 317. 
In these cases, the diaphragms may be regarded as compressed 
rings corresponding externally with the outline of the valves; but 
Heiberg has called attention to the fact that, in the case of Striatella, 
the diaphragms are somewhat differently constructed. ‘ Smith’s repre- 
sentation of the structure of this species is in the main correct, but he 
has misapprehended the form of the diaphragms, considering them to 
be closed rings (as his figure 307 h, as well as the descriptive term,. 
“ Annuh”’ indicate), whereas in reality they are open at one end. The 
form of them would naturally be best seen by preparing them out sepa- 
