570 Reviews. | July, 
the Super-Arctic Zone, the Highland forms alone occur. Thus, on the 
summit of Ben Maedui, only seven flowering plants are found, viz. 
Silene acaulis, Saxifraga stellaris, Salix herbacea, Luzula spicata, 
L. arcuata, Carex rigida, and Festuca vivipara. Along with them are 
associated Lycopodium Selago, and several other Cryptogamic plants. 
A complete list is given in the work of all the Phanerogamie and 
Cryptogamic plants of the counties, and full references to their localities. 
There is also a map of the district, with a delineation of the various 
zones of vegetation, and a notice of the plants which mark different 
altitudes. The ‘Guide’ is compiled with great care and correctness by 
one who is thoroughly conversant with the Flora, and who has for 
many years been in the habit of visiting the localities. Dr. Dickie 
has done good service to practical botany by this publication, which 
ought to be the pocket companion of every one who means to explore 
the floral treasures of the North of Scotland. 
BRITISH AND AMERICAN CONCHOLOGY.* 
WuHatEver may be the future destiny of those constituent groups 
which collectively form the genera of natural science, it is certain, 
that from the time of Linneus they have, in numberless instances, 
endured a considerable amount of severe cross-examination, and 
have stood their ground with much firmness. Species are indeed, 
at present, somewhat stubborn facts, and exhibit not a few very re- 
markable idiosyncrasies, which have to be disposed of before the 
theory of development can be regarded as perfectly established. 
To an unprofessional observer, the aspect of a named collection, 
in almost any branch of natural history, is very perplexing. In 
entomology, for instance, he may notice a series of insects, under the 
same specific name, yet differing from each other in size, colour, and 
even in form; whilst not far from these, two groups may appear, in 
one of which the specimens are so like those of the other, as to be 
apparently indistinguishable, yet he may find the groups marked by 
different specific, perhaps even by different generic, names. The 
arrangement may, nevertheless, be perfectly accurate and easily in- 
telligible to the entomologist, who, in a variable species, at once 
recognizes the specific identity of insects, differing at first sight, 
as much as a magpie does from a jay; whilst between two constant 
species, he knows the characteristic difference is very slight. We 
may be more or less inclined to attach importance to specific dis- 
* «British Conchology; or, an Account of the Mollusca which now inhabit 
the British Isles and the surrounding Seas.’ Vol. II., ‘ Marine Shells : compris- 
ing the Brachiopoda and Conchifera, from the Family of Anomiide to that of 
Mactride.’ By John Gwyn Jeffreys, F.R.S., F.G.8., &c. Van Voorst. 
‘Observations on the Genus Unio : together with Descriptions of New Species, 
their Soft Parts and Embryonic Forms in the Family Unionide.’ By Isaac Lea, 
LL.D., President of the Academy of Natural Sciences of Philadelphia, &e. With 
ten plates. Philadelphia : Printed for the author. 
