The object of this Catalogue is rather to enumerate all the forms 

 in a collection than to correct error, and therefore a large number of 

 names are retained as specific which I am myself unable to regard as 

 more than varietal. Authors have given them specific rank, and it 

 has been judged therefore better so to retain them here. Either 

 as "species" or as "varieties" modifications of form are always 

 interesting. 



My friend the Marquis di Monterosato, and some other writers 

 on Mediterranean Mollusca would seem to act upon the principle that 

 there is strong probability in favour of a shell found in the Mediter- 

 ranean being distinct from a closely allied Atlantic form, and hence a 

 slight amount of difference is regarded as specific. My own view 

 coincides with that of my regretted friend and companion in so many 

 dredging expeditions, the late Dr. Jeffreys, that when the little-known 

 Fauna of the West African coast, as well as that of Spain and Portugal 

 shall have been thoroughly investigaied it will be found that very few 

 true species will remain peculiar to the Mediterranean. 



The chief deficencies in this collection of Marine Mollusca occur 

 in the following groups : 



1. Mollusca of the North Eastern coasts of the United States. 



Attempts to obtain these have been singularly unfortunate. 

 The larger shallow-water forms have been procured partly 

 in exchange from the United States National Museum, but 

 chiefly by purchase from dealers. Hardly any of the minute 

 shallow-water species or of the deep-water shells are in my 

 collection. 



2. Cephalopoda and Nudibranchiata. Unfortunately, a large 



number of the latter collected long ago were found, when 

 unpacked after many years, to have been almost all lost 

 from evaporation of the spirit. 



3. Abyssal Atlantic and Mediterranean forms. 



4. Asiatic, Arctic and Alaskan species. 



INLAND MOLLUSCA OF THE PAL^ARCTIC REGION. 



I take this opportunity of mentioning as desiderata the Inland 

 Mollusca of those parts of Africa and Arabia which lie to the North of 

 the Tropic of Cancer; of Asia Minor, Persia, Afghanistan, and the 

 entire Russian Empire ; as well as those of the Azorean, Canarian, 

 and Cape Verde Islands. I shall be glad either to purchase these, or 

 to send in exchange for them European Land or Marine Mollusca. 



Catalogues already published : 



I. ECHINODERMATA. 



II. PANTOPODA. 

 III. CRUSTACEA. 



Febriiary 4, 1888. 



