426 DAVIDSON ON FOSSIL BRACHIOPODA. chap. xxii. 



selves, and then endeavor to imagine the number of forms 

 of the genus Bubus which may now exist, or probably have 

 existed, in Europe, and in regions intervening between Europe 

 and Australia, comprehending all which may have flourished 

 in tertiary and post-tertiary periods, we shall perceive how 

 little stress should be laid on arguments founded on the as- 

 sumed absence of missing links in the flora as it now exists. 



If in the battle of life the competition is keenest between 

 closely allied varieties and species, as Mr. Darwin contends, 

 many forms can never be of long duration, nor have a wide 

 range, and these must often pass away without leaving 

 behind them any fossil memorials. In this manner we may 

 account for many breaks in the series which no future 

 researches will ever fill up. 



Davidson on Fossil Brachiopoda. 



It is from fossil conchology more than from any other 

 department of the organic world that we may hope to derive 

 traces of a transition from certain tj^pes to others, and fossil 

 memorials of all the intermediate shades of form. We may 

 especially hope to gain this information from the study of 

 some of the lower groups, such as the Brachiopoda, which 

 are persistent in type, so that the thread of our inquiry is 

 less likely to be interrupted by breaks in the sequence of the 

 fossiliferous rocks. The splendid monograph just concluded 

 by Mr. Davidson, on the British Brachiopoda, illustrates, in 

 the first place, the tendency of cei'tain generic forms in this 

 division of the mollusca to be j)ersistent throughout the 

 whole range of geological time yet known to us; for the 

 four genera Bhynchonella, Crania, Discina, and Lingula have 

 been traced through the Silurian, Devonian, Carboniferous, 

 Permian, Jurassic, Cretaceous, Tertiaiy, and Recent periods, 

 and still retain in the existing seas the identical shape and 



