9 



names which have been widely quoted are also included. It must be 

 kept in mind, however, that this classification is purely tentative, and 

 that, with the exception of absolute synonymes, the discovery of the 

 character of an interior, or the more complete elucidation of the char- 

 acters of an obscure genus, may at auy time give it a standing to which 

 it is not at present entitled. For this reason, it is certain that no classi- 

 fication of so large a group of fossil forms as the Brachiopoda comprise 

 can be anything more than tentative for many years to come. 



The dates are in all cases intended to represent those of actual pub- 

 lication, a matter not always easy to determine. In some difficult cases, 

 where the date of presentation of a MSS. appears on the title page 

 without any reference to the actual date of publication, the former is 

 used as a numerator, and the earliest date for publication to which the 

 paper is known to be entitled as a denominator, of a fraction in the 

 date column. 



It will not be a matter of surprise that, in giving references for good 

 figures, the magnificent works of Mr. Davidson have almost constantly 

 been drawn upon. Students are to be congratulated that these are 

 among the most accessible works on the subject. 



Since Calceola has for so long a period been referred to as a Brachiopod, 

 or included with them, it has been decided to include its very copious 

 synonymy, though it is now known, through the researches of Dr. Lind- 

 strom, to belong to the Goelenterata. 



A bibliography was originally contemplated in connection with the 

 index, but it was soon found that, to make it complete, more time and 

 space would be required than could conveniently be devoted to it. 



It is hoped that few important mistakes exist in the list, though the 

 character of the references is such as to render the work particularly 

 liable to typographical errors. Not a few such errors which appear in 

 earlier works of t"he kind have been corrected, and the indulgence of the 

 reader is requested for any new ones which may unfortunately have 

 crept in. 



Eeferences have usually been made in a sufficiently full manner to be 

 readily identified; a few exceptions are, therefore, noted. 

 Dav. 1853 ; to A general Introduction to the Classification of the Brachiopoda, by Thcs. 

 Davidson, F. G. S. &c. ieing British Fossil Brachiopoda, vol. i, art. iii, Paleon- 

 tograpbical Society, Loudon, 1853, 4to. 



The references to the subsequent series of Monographs are made by the geo- 

 logical horizon ; as, " Mon. Silurian Brach. p." «fcc. 

 Dav. 1856; <o Introduction £t I'Histoire Naturelle des Brachiopodes Vivants etFossiles, 

 par Thos. Davidson, Esq. traduit de I'Anglais par MM. Deslongchamps : m 

 M6moires de la Soci<5t^ Linu6enne de Normandie, x, pp. 69-271, Caen, 1856, 4to. 



