454 Rev. Canon Norman's Revision 



5. The distribution of the testaceous species has been very 

 fully worked out by Jeffreys in ' British Conchology ' and 

 his subsequent papers. Distribution is for the most part only 

 given here for the additions to the British list ; nor have I 

 thought it necessary to add further localities for well-known 

 British species, except in the case of those which are most 

 rare. 



6. While the general arrangement of Fischer's ' Manuel de 

 Conchyliologie ' has in the main been adopted, it has in many 

 points been departed from. Perhaps the chief of these is that 

 Fischer has not been followed in dividing the Pelecypoda 

 into the orders Tetrabranchiata and Dibranchiata, since such 

 an arrangement in many cases widely divorces genera which 

 seem in most points to be nearly related. I have here adopted 

 the more recently expressed views of Dr. Dall. 



7. Certain groups, such as the Pleurotomidse, the Rissoidas, 

 and the Gymnoglossa, present unusual difficulties in arrange- 

 ment by their shells, difficulties which can only be removed 

 when we have become much more fully acquainted with the 

 animals which form them. I have done the best I can with 

 these groups, but am far from satisfied with the results. My 

 endeavour has been to steer a middle course between those 

 conchologists who excessively multiply genera and the 

 arrangement of Jeffreys, who, in my opinion, made his genera 

 too large — a course which he, subsequently to the publication 

 of ' British Conchology,' most markedly departed from. 



The British Area. 



The area regarded as British is that which I have indicated 

 in a paper on the subject printed in last month's number of 

 this Journal ('Annals,' May 1890), where it is thus defined: — 

 South. — By lat. 49° 30' N., which parallel passing east- 

 wards terminates at long. 5° W., or midway between the 

 Land's End and Brest. Thence mid-Channel is followed 

 until lat. 51° 50' N. is reached off the east coast. 



East.— From lat. 51° 50' N., long. 2° 30' E. is taken as 

 the eastern boundary northwards. 



North. — Lat. 60° 0' N., coming from the west as far as 

 long. 5° 0' W., thence due north-east to long. 1° 0' W., 

 thence due east to meet the eastern boundary at 2° 30' E. 

 West. — Down to the base of the continent at 1500 fathoms. 



