Limits of Species in the Biatomacese. By Thomas Comber. 463 
necessary to unite them. Thus Dr. Cleve * reduces to varieties of 
Colonels Liber the following species of Prof. Grunow : Navicula 
linearis , I860, N. bicuneata, 1860, N. excentrica, 1860, and N. elon- 
gata, 1864 ; and, indeed, Prof. Grunow has himself seen fit to reduce 
to varieties forms which he originally regarded as distinct species. In 
his work on the Caspian Diatoms (1878) he expresses the following 
view regarding species : “ I have discussed the preceding group (that 
of Nitzschia Sigma) because, like so many others, on more extended 
examination, it convinces us that previously conceived notions of 
species ar8 untenable. Certainly hardly any one would consider 
such extreme forms as N. maxima and N. anguillula or N. Clausii as 
belonging to the same species, and yet there exists between them an 
uninterrupted connection. It is, however, truly an altogether idle ques - 
tion whether this or that form should be considered as a species, sub- 
species, or variety, the important point in systematic natural history 
being to discover the connection between organic forms ; and for this 
is required yet much more protracted and thorough study. But, 
where the connection of a large group is clearly known, this should 
be indicated in the nomenclature ; and this can only be effected by 
the utmost possible extension of the conception of a species, and the 
arrangement of all related forms as varieties ; whether this or that, 
the one or the other, be regarded as good or as intermediate species.” t 
Numerous species have also been established by Adolf Schmidt, 
whose beautiful and accurate figures are so valuable a record of forms, 
and so great an assistance in identification. He explains quite 
candidly the principle upon which he has worked : “ Cleve refers all 
(the) forms 7-18 to C. heteroidea. No one can expect that I can 
agree to this, since I have for already forty-four years, on the ground 
of quite* irrefutable facts, rejected the Lamarckian mania for combina- 
tion, at that time believed, as an offence against science ; have com- 
pletely converted the most pronounced Lamarckian, Bossmasler ; and 
have recommended as the first duty of naturalists, the strict emphasis- 
ing of perceptible distinctions.” 
In the earlier part of his Atlas, he rightly figured many doubtful, 
or, as he calls them, “ critical ” forms, without naming them, leaving 
it to be decided, from further observation of specimens, whether or 
not they were regarded as entitled to specific rank. But, as later 
authors did not hesitate to confer on the forms he figured names of 
their own, even when they had not even seen a specimen, but knew 
the forms only from his figures, he felt himself compelled to attach 
specific names to all his figures. He has done so even when the 
forms represented approach so closely to each other as those repre- 
sented on plates 194-6 of the Atlas, related to Cocconeis pellucida, 
C. pseudomarginata, and C. heteroidea , many of which Dr. Cleve 
refers to the last named species. 
* ‘ Synopsis of the Naviculoid Diatoms,’ part i. (1894) pp. 54-5. t P. 28. 
