XV] CLASSIFICATION 37 5 



Brachiopods are found in all seas. About eleven genera have 

 . been dredged around the British Isles, most of them 



Distribution . . 



andciassifica- in comparatively shallow water. Lingula is usually 

 found between tide-marks or in shallow water; it lives 

 in a tube in the sand, and the bristles round the mouth of the shell 

 doubtless serve to keep out particles of sand which might otherwise 

 injure the animal. It is found along the East coast of America, in 

 the Pacific and other places. One species of Brachiopod, Tere- 

 bratala wyvillei, has been dredged from a depth of close upon 3000 

 fathoms. 



Perhaps the chief interest of the group is that it includes an 

 enormous number of fossil forms which had a very wide distribu- 

 tion. The extinct forms far surpass both in variety and number 

 the existing forms. Some species have lived on, as far as we can 

 judge from the shell, unchanged from the time when the earliest 

 fossil-bearing rocks were laid down. They may thus claim to be 

 one of the oldest groups with which we are acquainted. 



The Brachiopoda are classified as follows : 



Class I. ECARDINES. 



Shell with no hinge and no internal skeleton. The alimentary 

 canal has an anus. 



Ex. Lingula, Crania. 



Class II. TESTICARDINES. 



Shell with hinge and internal prolongations, chiefly calcareous. 

 No anus. 



Ex. Terebratula, Argiope, Waldheimia, Rhynchonella. 





