100 ' POPULAR BllITISH CONCHOLOGY. 



connecting links between them^ and only serve to show how 

 impossible it is to seize any characters sufficiently permanent 

 and absolute^ to form any distinct line of demarcation be- 

 tween one group and another in nature. In the *" History of 

 British Mollusca' the following characters are given, for the 

 purpose of uniting the different groups under one family: — 

 " All the tribe have the mantle freely open, no tubes, a small 

 or obsolete foot, probably caj)able in some stage of the ani- 

 maFs existence of spinning a byssus, and constantly doing 

 so in some species, united adductor muscles, leaving a single 

 impression in the shells, and a ligament wholly or partly in- 

 terior, lodged in a cardinal groove and sometimes accom- 

 panied by teeth/^ 



The two adductor muscles of other bivalves, being in the 

 Ostraadm united into one, and producing one impression 

 in the shell, is the most important character of the family. 



PEC TENS, OB SCALLOPS. 



I. Lima. — ^' Oh, here is the Lima's nest V is the delight- 

 ed cry of Miss Alder, when, dredging with her papa and 

 the Eev. D. Landsborough, she reaches a little cluster of 

 broken fragments of coral bound together in a mass; and 

 opening the lump, there is the Lima snugly ensconced in the 



