462 
Transactions of the Society. 
Mr. Raffs, when writing the section on the Diatoms for Pritchard’s 
‘ Infusoria,’ 1861, rejected certain characters, in the recognition of 
which Smith had followed Ehrenberg, e.g. the number of rays, or of 
processes, in the disciform genera, and of dorsal elevations in the 
genera Eunotia and Himantidium. He therefore constituted such 
species as Actinocyclus Ehrenbergii (already mentioned), Eunotia 
Ehrenbergii, under which he placed 14 of Ehrenberg’s species, and 
Eunotia robusta, including 14 of Ehrenberg’s species. The follow- 
ing quotation is sufficient to indicate his view on the subject imme- 
diately under consideration : “ Surirella lata differs from S. fastuosa 
in its form, and usually in its larger size, but the markings are similar 
in both. As Prof. Gregory finds intermediate states, they may he, as 
he supposes, mere varieties.” * 
Dr. Gregory, although a good many of his species, especially of 
Amphora , have been united by later authors on the detection of con- 
necting forms, nevertheless held the broad view of species. In his 
paper on the ‘ Diatoms of the Clyde ’ t he writes as follows : “ In 
many species, though by no means in all, the shape as well as the 
size of the forms, and even the striation, all vary to a great extent. 
In such cases it is most important that every author should figure a 
sufficient number of selected forms to show the real extent of the 
species. These variable species ought to be thus treated individually, 
by which means many existing species would he got rid of and re- 
duced to a smaller number.” 
Among the many species published by Dr. Greville are some 
which later observers have found to rest on insufficient characters, or 
have joined together, on proof that they belong to only one species, as, 
for instance, his Triceratium Hardmanianum, T. trilineatum, and 
T. acceptum, which, along with the previously published T. radiatum 
Brightwell, are only the upper or lower valves, or inner or outer 
plates of one form, for they have all been observed by Prof. Brun 
together in a single filament. But Dr. Greville’s conception of a 
species did not differ materially from that of the authors already men- 
tioned. Nowhere does he knowingly propose to separate as species 
more than one form belonging to a continuous series. 
Dr. Heiberg also regarded species as comprehensive, and founded 
such aggregates as Cymbella encyonema , G. variabilis, Cocconeis com- 
munis. 
A great change in the valuation of species becomes perceptible in 
the writings of Prof. Grunow, at any rate in those published up to 
1880. His species are very numerous, but are frequently based 
upon comparatively trivial characters. In his revision of the genus 
Nitzschia,t many of the species, described and named, differ extremely 
little from others, and are indeed frequently, by his own admission, 
of an intermediate character. His species of Navicula, too, are often 
open to the same objection, so that later authors have deemed it 
* Pritchard’s ‘ Infusoria,’ p. 797. f 1857, p. 63. % 1 Arctic Diatoms,’ 1880. 
