PREFACE. 



This Manual, Tvhich for six years occupied tlie 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, William Lon^sdale — ■ 

 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 

 Mollusca." 



That he 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. Owex in the Hunterian 

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

 Baleoue in the Madras Museum ; by the Eev. Prof. Hexslow, 

 in his Report to the British Association on the Eormation of' 

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

 British Fossils. 



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

 b 



