ADVERTISEMENT. 



The materials from which the following Monograph has been drawn up have been 

 afforded by the copious and valuable collections of Crag Polyzoa placed, with tlieir wonted 

 liberality, at my disposal by Mr. Searles Wood and Dr. Bowerbank. 



The work was originally undertaken by the late much-lamented M. Jules Hairaes, 

 but he was unable even to commence it before death put an end to the labours of one 

 whose accurate knowledge and practised observation of similar fossil remains would have 

 enabled him to treat the present subject far more satisfactorily than it has been in mv 

 power to do. 



Though long accustomed to the study of recent Polyzoa, until the present undertaking 

 was commenced I had formed but an imperfect idea of the difficulties attending the inves- 

 tigation and accurate discrimination of fossil forms. 



With respect to the synonymy of species, so little assistance, with regard to the more 

 minute though essential characters, can in most cases be derived from published descrip- 

 tions and figures, with the sole exception almost of the admirable works of Hagenow and of 

 Reuss, that it is almost impossible to arrive at any certainty without the direct comparison 

 of specimens. And though no endeavours or time have been spared in the elucidation of 

 this part of the subject, I am fully conscious that it still remains in an unsatisfactory state. 

 In order to obviate some of the difficulties above referred to, the utmost care has been 

 taken in the drawing of the figures to render the characters as clear and distinct as the 

 condition of the specimens would allow. This could only be done by the adoption of a 

 scale somewhat larger than that usually employed. It is consequently to be hoped that 

 future inquirers will at any rate have little difficulty in recognising the species here 



intended. 



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