PREFACE. 



This 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 lahour and expense which 

 only a very extended circulation will repay. 



The plan and title were taken from the ''Manuel des 

 Mollusques" of M. Sander Eang, incomparably the best 

 work of its kind — for an acquaintance with which the author 

 was indebted to his friend and master, "William Lonsdale— 

 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. Edwaed Foebes ; 

 without whose approval he seldom added to, or deviated 

 from, the practice and plan of the "History of British 

 MoUusca." 



That be was right in taking this course, has been sanctioned 

 by the highest authority in this country ; — since the same 

 scheme has been employed by Prof, Owen in the Hunterian 

 Lectures and Catalogue. It has also been adopted by Dr. E. 

 Balfotje in the Madras Museum ; by the Eev. Prof. Henslow, 

 in his Report to the British Association on the Formation of 

 Typical Collections ; and by Prof. Morris in his Catalogue of 

 British Fossils. 



It was the writer's desire, by abstaining from the intro- 



b 



