ill!Ill

236
NKIDIUM.
N. Hyalosira Cleve. (in Le Diat, i., p. 77, pi. 12, f. 11*), plate
27. fig. 786.
Valve convex, thin, lanceolate, rostrate or with rounded apices ; striae
punctate, 29 in 1 c.d.m. Frustule quadrangular, connecting
numerous pleats. Length, about 2 c.d.m. Frustule feebly silicious.
zone with
Marine. Month of the Tay, Scotland (Cleve and Moller, No. 309 !) Cresswell, Northumber-
land, England (Deby.).
Neidium Pfitzer. (1S71. Ueber Bau und Entw. d. Baa, p. 39).
This very natural group corresponds to my Affines ;
it is based on the
form of the endochrome, on the apices of the raphe near the central nodule
being turned in opposite directions, on the striation of the valve being often
oblique, and on this striation being frequently interrupted by one or more
longitudinal sulci.
Pinnularia Ehr. (1840). Valve furnished with costae and not
striae. This genus corresponds to my group Pinnularia. Former authors
also included in it the Radiosce, whose striae could not then be resolved into
beads.
Rhaphidodiscus Th. Christian (1887, in the Journal "The
Microscope," p. 67).
This genus is, according to Mr. Deby, based on the
accidental position of a Navicula in a valve of Melosira. It
is also perhaps founded on a disciform Navicula,
such as
that represented in Fig. 33 at the side. This figure, which
corresponds very well with that of Mr. Christian,
from one of my photographs, and reproduces
found by Mr. Weissfiog in material from Naparima
^. ./ig. 33. j slan(j f La Trinite, Antilles.
Discnorm Aavicula.
is drawn
a valve
in the
Lately, Prof. Brun, having been good enough to lend me the photographs
and preparations which he received from Mr. Christian, I have been able to
assure myself that the Naparima diatom in no wa> differs from that of Mr.
Christian's specimen, which is a genuine Navicula. Mr. Deby's explanation
is the only one that satisfactorily explains the figure published by Mr. Christian.
We have reproduced this as figure 913 on plate 35.
Schizostauron Grun. (1867, in Hedwigea, p. 28).
A genus containing eight species, all from the South of Europe, or Extra-
European. Round the central nodule is a blank space, stauroneiform (or a
true stauros ?), bifurcated into a St. Andrew's cross.
Stauroptera Ehr. (1843).
Group including all forms possessing a pseudo-stauros.
Stictodesmis Grev. (1863), South Pac. Diat., p. 30.).
Based on the craticular state of the valve, analogous to Craticula. Fig. 34
represents Stictodesmis Australis Grev., the most common form of this genus.