PREFACE. 
Tuis Manual, which for six years occupied the Author’s 
unceasing attention, was intended as a companion to Gen. 
Portlock’s Geology ; and the desire to make it worthy of that 
association led to an amount of labour and expense which 
only a very extended circulation will repay. 
The plan and title were taken from the ‘‘ Manuel des 
Mollusques”’ of M. Sander Rang, incomparably the best 
work of its kind—for an acquaintance with which the author 
was indebted to his friend and master, Witt1am LonspstE— 
the founder of the ‘‘ Devonian System” in Geology. 
On the subject of classification and nomenclature the Author 
followed the advice and example of his former colleague in 
the Geological Society, the late Prof. Epwarp Forpss; 
without whose approval he seldom added to, or deviated 
from, the practice and plan of the ‘‘ History of British 
Mollusca.” 
That he was rigkt in taking this course, has been sanctioned 
by the highest authority in this country ;—since the same 
scheme has been employed by Prof. Owzn in the Hunterian 
Lectures and Catalogue. It has also been adopted by Dr. E. 
Barrourin the Madras Museum; by the Rev. Prof. Hznstow, 
in his Report to the British Association on the Formation of 
Typical Collections; and by Prof. Morzts in his Catalogue of 
British Fossils. 
It was the writer’s desire, by abstaining from the intro- 
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