﻿204 T. Davidson — What is a Braohiopod? 



my monograph on "British Fossil Brachiopoda." ^ I then published 

 my views, which were subsequently -wery generally adopted both by 

 British and foreign palseontologists ; but I did not omit to impress 

 ■upon my readers that we were not then (neither are we now) in a 

 condition to prepare a complete or satisfactory classification of the 

 numerous species composing the class. In 1853 I divided the 

 Brachiopoda into eight families comprising twenty-four genera and 

 twenty-two sub-genera ; but, during the years that have elapsed since 

 that date to the present time, about seventy more genera or sub- 

 genera have been described. I published a list of them in the Sussex 

 Daily News for the 20th of August, 1872, and they will be found 

 recorded in the table accompanying this memoir, where their geo- 

 logical distribution in time has iDeen tabulated, as far as the present 

 state of our information will permit. It it, however, very probable 

 that a certain number of the names there recorded will have to be 

 placed amongst the synonyms, and it is of the utmost importance 

 that genera should not be founded on trifling modifications, or un- 

 important details which exist only in some abnormal forms. In 

 1855,* I proposed certain modifications in the arrangement published 

 in 1853 by getting rid of the sub-families. Much consideration on 

 my part has been devoted to the subject; but I feel that in order to 

 place the known genera and species in their respective families, or 

 into new ones that will have to be created, much more informa- 

 tion must be acquired. The subject is immense when one has to 

 grapple with between 5000 and 6U00 described species, varieties or 

 synonyms ; and it must likewise be remembered that many of the 

 extinct genera have as yet been but imperfectly elaborated. The 

 material in hand is, however, so great that doubtless, in time, 

 palfeontologists will be able to lay before the public a complete 

 history of a class, which, as will be shortly shown, has played an 

 important part in the great life-system of our globe, from its dawn 

 to the present time. It will be necessary, I think, as has already 

 been stated, to admit the two great divisions, Tretenterata and Clisten- 

 terata, into any scheme of classification, although it is impossible to 

 say whether all the extinct genera were provided with an anal 

 aperture, or otherwise. 



The Tretenterata would comprise the families Zingulidce, 

 Discinidce, Craniada, and perhaps one or two others. 



The Clistknterata would include the families Terebratulidm, 

 Thecidcedce, Spiriferid(S, Bhynehonellidce, Pentameridce, Orthidce, 

 StrophomenideB, Froductidce, and perhaps two or three others that will 

 have to be characterized. By far the larger number of described 

 genera and species would find their places in this last great division 

 and the above-named families. We will now, very briefly, notice 

 some of the characters of the families above indicated. 



* A French revised translation of my general introduction by MM. Deslongchamps, 

 father and son, will be found published in vol. x. of the Memoires de la Society 

 liinn^enne de Normandie, 1856. — A German translation by Prof. E. Suess and Count 

 Marschall was also published in Vienna in the same year, 1856. 



* Annals and Mag. of Nat. Hist. 2ud ser. vol. xvi. 



