ADVERTISEMENT. 



I propose to compile a Conchological Manual, which, whilst more compre- 

 hensive than any similar work hitherto published, shall be so condensed in 

 text and illustration that it may be issued at a much more moderate price. It 

 will include, in systematic order, the diagnoses of all the genera and higher 

 divisions of the mollusca, both recent and fossil, and the descriptions and 

 figures of all the recent species ; together with the main features of their 

 anatomy and physiology, their embryology and development, their relations to 

 man and other animals, and their geological and geographical distribution. 



The material at my disposal for the purpose of working up this comprehen- 

 sive plan is ample and unexcelled : 



I. The Library of the Academy of Natural Sciences of Philadelphia con- 

 tains almost every separate work ever published upon the subject, together 

 with the various volumes of voyages and travels, of general natural history, 

 and especially scientific periodicals, and the published transactions of learned 

 societies throughout the world. For Conchological purposes this library is 

 almost complete, and it is very rarely that its shelves do not afford any 

 reference desired. 



II. The Conchological Museum of the same institution ranks among the 

 largest in the world in the number of species represented, whilst in the rich- 

 ness of its geographical suites, the number of specimens illustrating varietal 

 forms, etc., it is probably the finest collection extant. 



It is intended to arrange and describe the valid species in accordance with 

 their inter-relationships, and it is hoped that by so doing their number may 

 be greatly reduced. Every genus and every recent species will be fully 

 illustrated, so far as specimens or hitherto published figures will enable me to 

 do so. The expet'ienced skill of Dr. E, J. Nolan, who has undertaken to 

 furnish the illustrations (of which 30,000 to 40,000 will be required), will 

 sufficiently guarantee the accuracy of this department of the Manual. 



In the preparation of the text evei*y care will be taken to discover and 

 correct, and to avoid, error; but it may be reasonably apprehended that the 

 performance of such an immense work must be in many respects inferior to 



