YEKMES AND MOLLUSCA OF THE DEEP SEA 115 



development information that will probably shed 

 much light on the relationships to one another of the 

 many groups of Vermes. Their occurrence in water 

 of moderate depths only indicates perhaps that they 

 are gradually being crowded out from the more 

 favourable localities of shallow water, and are tending 

 towards extinction on the one hand, or a deep-sea 

 habitat on the other. 



The Brachiopoda need not detain us long. Some 

 species are capable of existing at a great variety of 

 depths without any observable modification of shape 

 or characters. Thus Terebratulina caput serpent'^ 

 has the extraordinary bathymetrical distribution of 

 0-1,180 fathoms, and Terebratula vitrea 5-1,456 

 fathoms. Atretia is the only genus peculiar to deep 

 water. It is a noteworthy fact in connection with 

 this order that the two genera, Lingula and Glottidia, 

 which compose the sub-order Ecardines, are both 

 confined to shallow water. Now the Ecardines are 

 anatomically, at any rate, the most primitive of the 

 Brachiopoda, and Lingula has the most ancient 

 geological history of any living genus of the animal 

 kingdom, shells almost, identical with those of the 

 living species being found abundantly in the Cambrian 

 strata. Why it is that Lingula has been able to 



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