204 
T. Davidson — What is a Brachiopod ? 
my monograpli on “ Britisli Fossil Brachiopoda.” 1 I then publislied 
my views, which were subsequently very generally adopted both by 
British and foreign pakeontologists ; 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 tbe 
numerous species composing the dass. 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 been 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, 2 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 6000 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, 
palasontologists will be able to lay before the public a complete 
history of a dass, 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 Lingulidce, 
Discinidw, Craniadce, and perhaps one or two others. 
The Clistenterata would include the families Terebratulidce, 
Thecidcedce, Spiriferidce, Bliynchonellidee, Pentamer idw, Orthida, 
Strophomenidce, Productidw, 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. 
1 A French revised translation of my general introduction by MM. Deslongcliamps, 
fatlier and son, will be found published in vol. x. of the Memoires de la Socidtd 
Linndenne de Normandie, 1856. — A German translation by Prof. E. Suess and Count 
Marschall was also published in Vienna in the samc year, 1856. 
2 Annals and Mag. of Nat. Hist. 2nd ser. vol. xvi. 
