On the Classification of the Diatomacese. By M. Paid Petit. 69 
making two median lines and four margins, in all sis lines, which, as 
the valves are very pellucid, are seen all at once in the frustule, but 
the valves show the real structure.” 
The descriptions are equally inaccurate and obscure. The 
Kev. W. Smith merely remarks that “ The frustules (? valves) are 
linear lanceolate, length • 0033' to • 0034',” a description that applies 
to scores of Naviculoid forms. 
The species A. paludosa was considered by the late Professor 
Walker Arnott to be merely a delicate variety of A. alata. The 
form of the valves in both species is difficult to understand when 
examined with a monocular only, but with a binocular and a 4-inch 
objective it is easily made out. The keel consists of a thin plate or 
ribbon of silex appearing when the frustule is seen in f. v. like 
a double arch, the central depression sometimes showing traces of 
a central nodule. In A. paludosa the four arches of the frustule 
are reflexed or bent over in opposite directions ; in A. alata and 
A. ornata they are more nearly at right angles to the surface of 
the valve. The presence of a keel is in fact the principal dis- 
tinction between Amphiprora and Scoliopleura Grunow. Amphi- 
prora latestriata of de Brebisson is Scoliopleura convexa ( Navicula 
convexa of Wm. Smith), and not Nitzschia bilobata, as supposed by 
the author of the ‘ Synopsis ’ and Mr. Balfs. The nearest ally to 
Amphiprora is probably Donkinia. — F. K.] 
6th Tribe, Nitzschie.®. 
The Nitzschiete offer the greatest variety in the form of the 
frustules ; they all have a punctate keel and a single layer of 
endochrome with central elliptical opening. The relation of the 
endochrome to the valves offers three modifications. 1st. The 
parts of the zone are so compressed that there remains but little 
space for the layer of endochrome, which in consequence traverses 
the frustule diagonally (13) from one keel to the other. It is 
this group that forms the connection with the Amphiproreae. 
2nd. The layer is very small, and is completely divided by the 
central elliptical opening. 3rd, and lastly. The layer of endochrome 
rests on one of the sides of the zone, and covers the two adjacent 
valves (Figs. 11, 12, 13). Among the Tryblionella, a genus of 
which M. Pfitzer does not speak, the endochrome, so far as I 
have verified it in T. constricta Greg., and T. Hantzscliiana Grun., 
presents the same disposition as in the third group of Nitzschieae. 
Genera, Nitzschia, Ceratoneis, Tryblionella. 
[The first group belongs to my genus Perrya.* When I de- 
scribed the species P. pulcherrima, I had not seen the s. v., 
which is very narrow ( ■ 0005 to * 0007 of an inch in breadth), 
linear with acute apices. A line of large distant granules 
traverses the centre of the valve from apex to apex. The diagram, 
* ‘ M. M. J.’ vol. xi. p. 218. 
