Mr. F. P. Pascoe on the Genus Dicranocephalus. 23 
smooth, distinctly (but not deeply) vermiculate: I have seen, in Dr. 
Powers’s cabinet, a similar and equally interesting connecting link 
between the two forms of females of Dytiscus cirewmeinctus. 
H. Shuckardit is in the cabinets of the British Museum, Oxford 
University, Mr. Bakewell, Dr. Schaum, Mr. Waterhouse, and the 
Rev. Hamlet Clark. 
IV.—On certain additions to the Genus Dicranocephalus. 
By Francis P. Pascor, F.L.S., &e. 
Tue reality of the existence of species has been questioned by many 
naturalists ; not, however, in the Darwinian sense—that is, that as 
all organic beings have descended from “some one primordial form,” 
they only differ from each other in degree, and, therefore, that 
classes, orders, families, genera, and species only exist as artificial 
combinations,—but in the sense of “ special creations,” and the im- 
possibility of drawing any satisfactory line between species and 
varieties. 
The disbeliever in the material existence of species, however, need 
not abandon the use of the term: as Agassiz has remarked, “species 
exist as categories of thought, in the same way as genera, families,” 
&c.; and the only difference between a species and a variety appears 
to be, that in the first the distinctive characters are more important 
or more numerous than in the second, and are not bridged over by 
intermediate gradations, as is frequently observed in the variety. 
Latterly the word subspecies has been adopted to express a grade be- 
tween species and variety, but at the same time it has been generally 
connected with, or assumed to be limited to, a certain geographical 
area. As I take it, the subspecies being dependent for its differential 
characters on physical, perhaps combined with other causes, and those 
causes being removed, it would return sooner or later to the normal 
condition of the species from which it had originally been derived. 
The species of many genera are, however, so homomorphous, as often 
to suggest the idea of their having had a common parentage ; and no 
doubt it will be found to be so in many cases where their describers 
have been but too ready to consider the slightest variation of specific 
importance*. 
* A striking instance of this occurs in Paludomus aculeatus, a river shell of 
Ceylon, which, according to Mr. Blanford, in a communication to the Linnean 
Society, has been split into no less than twenty-four species, all of which he demon- 
strated, by a large series of specimens exhibited at the meeting, to be reducible to 
one! (Trans. vol. xxiii. p. 603.) 
