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PREFACE. 



T>Y a 'type' is meant the original specimen to which any 

 -*-^ generic or specific name was first assigned. Subsequent 

 observers in examining specimens which agree in general 

 characters with an already described form, often notice differ- 

 ences which may indicate a new species, may be only due to 

 incomplete description, or to the imperfect state of preservation 

 of the type. In order to determine these points, it is necessary 

 for them to see the actual fossil, which the author of the species 

 had before him, when he wrote his description. 



The importance of preserving and distinctly marking figured 

 and described specimens, has only of late years been generally 

 realised. A committee of the British Association reported 

 upon the subject last year'. In the Woodwardian Museum 

 such specimens have been mounted on tablets of a special 

 colour, — at first pink was used, but now blue, a more stable 

 colour is being substituted. The plan of exhibiting all the 

 types by themselves, on the top of the cabinets was tried, and, 

 except where they are mounted on coloured tablets, this method 

 can be recommended, as in every museum of importance, 

 inferior specimens are continually being replaced by better 

 ones, and thus the type, which is sometimes a poor specimen 

 may perhaps get lost sight of. As soon however as the types 



» Bep. Brit. Aeaoc. (Leeds), 1890, p. 339. 



