CONCLUSION. 345 



the road leading from Solva to Whitechurch, St. David's ; and, if it should turn out to 

 be the same as the shell under description, which it resembles, it will be the oldest known 

 form of the genus and one of the earliest Brachiopoda on record. Discina ^MgoIms has 

 also been found by Mr. Belt in the Maenevian stage at Camlan, in North Wales. 



CONCLUSION. 



I HAVE now described and ilhistrated all the British Silurian species of Brachiopoda 

 of which I could procure examples ; and, although the material kindly furnished to me 

 from many public, as well as private, sources has been very great, it has unfortunately 

 in many cases been insufficient to enable me to do as much justice to every part of 

 the subject as could have been desired. No Palaeontologist will, however, feel surprised 

 at such a statement ; nor could any one expect that the first attempt at a Monograph of 

 so extensive a group of fossils as the one entrusted to my elaboration could be entirely 

 successful, or that I could fully describe and illustrate a number of forms hitherto known 

 by a few imperfect specimens or casts only, and these, in some cases, of only one of the 

 valves. In order to be able to appreciate the real specific value of any form, a matter 

 difficult under any circumstances, it is necessary to be provided with a sufficient number 

 of specimens showing the modifications assumed by the exterior of both valves, as well 

 as that presented at various stages of the animal's growth. The interior of both valves 

 of the shell itself, or its representatives on sharply marked internal casts, is also absolutely 

 necessary ; and for a large proportion of our species such material has not yet been 

 forthcoming. Hence with reference to these last we cannot correctly appreciate their 

 specific claims. I have, nevertheless, been compelled, for reference-sake, to allow 

 them to retain provisionally a distinctive designation. It is highly probable, I may say, 

 if not quite certain, that, when better known, the two himdred and eight so-termed 

 species of Silurian Brachiopoda described in this Monograph will require to be 

 reduced in number ; and I would earnestly entreat Geologists and collectors of fossils, 

 who may be advantageously situated, to search for more satisfactory material relating to 

 the imperfectly known species and varieties, of which they will find incomplete descrip- 

 tions and illustrations in this Monograph. 



I should desire them to look upon this, as well as upon the whole series of my 

 Monographs, as a bold outline sketch, and not as a finished picture, and as still demanding 

 much labour and research, from many experienced hands, before it can be regarded by 

 the Scientific Public as in any way approaching to a complete work. That such may 

 be accomplished with time, patience, and labour cannot be at all doubted. The material 

 required exists, but is still hidden in the rock, and may be disclosed by the careful and 

 discriminating use of the geological hammer. This should stimulate many a young 

 Geologist to search for the missing links ; and their efibrts will surely result in some useful 



44 



