170 Transactions of the Royal Microscopical Society. 
•008 mm., above '019 mm., summit more rounded than in 
S. cuneata. 
The genus Sceptroneis Ehr. is only distinguished from Synedra by 
its cuneiform valves. It contains the following species : Sceptroneis 
caduceus Ehr., S. clavata Greville, S. Gomphonema Jan. et 
Bab., S. cuneata Grun. et var. Javanica, S. dubia Grun., and 
perhaps S. marina Greg. = Meridian marinum Greg. Cam- 
pylostylus striatus Shadbolt ( Synedra Normaniana Greville) 
occurs now and then in the Honduras gathering, but I am 
uncertain whether this species should be placed in the genus 
Synedra or with Ceratoneis arcus. The latter is distinguished 
from Synedra by its curved valves and very distinct pseudo- 
nodules. [I am not prepared to admit that the forms now described 
are rightly placed in the genus Sceptroneis ; if striation has any 
distinctive value, they certainly are not. Herr Grunow’s figures show 
that the transverse lines are composed of short lines like those on 
Synedra robusta ; those on Sceptroneis caduceus are composed of 
large distinct moniliform granules like those on Doryphora 
amphiceros. Professor H. L. Smith unites Sceptroneis with 
Synedra.— F. K.] 
I have removed from Ceratoneis all the other species that I 
had united with it several years ago, and consider G. arcus the 
only representation of the genus. Eunotia ( Synedra ) lunaris and 
its varieties, as well as E. Jiexuosa, E. biceps, Breb., &c., are true 
Eunotiae, having the terminal nodules and the longitudinal line 
situated near the lower (central) margin of the valve, and no trace 
of a (central) pseudo-nodule like Ceratoneis arcus, and many species 
of Synedra. In Ceratoneis and Synedra the median line and 
terminal nodules are central. Schumann has delineated something 
like a central median line in some of the species I had erroneously 
placed in Ceratoneis and Kutzing in Synedra, but I have never 
seen it, and am of opinion that these details are about as correct as 
several other things delineated by Schumann, who seems to have 
been sometimes deceived by an excess of sunlight or other causes 
in the interpretation of minute structures. 
A remarkable example is the duplication of the striae of many 
diatoms, but which can only be seen in entire frustules when the 
focus of the microscope is situated exactly between the two valves 
(this fact was communicated to me by Professor Pfitzer, who had 
also observed it). Every line is then divided by diffraction 
into two, and every dot into : : . The latter phenomenon is 
very interesting, and may be easily seen in some of the larger 
species of Cocconema (Cocconema mexicanum, Ac.), with coarse 
granulations. 
I cannot avoid noticing here the exceedingly fine striation 
which Schumann has delineated on the smooth parts of some of 
