BRITISH SILURIAN BRACHIOPODA. 231 



being so nearly related, it is not to be wondered at that we should find so many of the 

 species to be common to both. 



The Upper and Middle Caradoc in Scotland are also very rich ; but, as far as our 

 present knowledge will carry us, are not quite as rich as the Llandeilo seems to be. The 

 Lower Caradoc is badly represented. 



In Scotland the Llandovery has afforded us some 4G or 47 species. These are 

 distributed as follows : 



18 in Lower Llandovery. 



27 in Middle Llandovery. 



34 in Upper Llandovery. 



Of these 12 seem common to the Lower and Middle Llandovery, 16 are common to 

 the Middle and Upper Llandovery, and about 9 to the three divisions. 



The Wenloch in Scotland seems poorly represented, while the Ludlow is well developed 

 and has afforded some 28 species, a large proportion of which are likewise found in the 

 Wenlock of England. 



These estimates and numbers, as I have already said, must be taken as essentially 

 provisional^ or as near as could be arrived at with the incomplete material in our 

 possession. Further collecting and more extended study of several of the species 

 enumerated in our Tables will also certainly tend to modify the numbers we have given, 

 which are only the result of my own investigations. 



I have now come to the end of my long series of Supplements, and in reality of the 

 Monograph, as far as I am able to make it with the material at my command. Every 

 now and then as our rocks continue to be searched, new forms will turn up which will 

 require to be described and illustrated. Specimens also will be found more complete of 

 a number of those imperfectly described, and these will form the subject of future 

 Supplements. 



I began visiting locaHties and collecting British Brachiopoda as far back as 1835. 

 The first plate relating to this Monograph was drawn on stone and submitted to the 

 Council of the Palseontographical Society in 1849; and the first part of the work was 

 printed in 1850, and issued in June, 1851. Since that period I have never relaxed in my 

 efforts to grapple with the large and very diflBcult subject that has been entrusted to my 

 care. Sorry indeed am I to be compelled to admit that, although very much progress has 

 been effected in our general knowledge of the Brachiopoda, and of British species in 

 particular, very much must, for the present, be left in an incomplete and unsatisfactory 

 condition — and this from want of the necessary material which has still to be discovered, 

 and which time and fortunate circumstances alone can reveal. 



Many unavoidable mistakes and shortcomings occur in the old Monograph, some of 



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