T. Davidson — What is a Brachiopod ? 
267 
ciating the Tretenterates with the larval star-fish, rather than with the annelids in a 
similar stage, or the adult forms of polyzoons. The latter seem to be more removed 
from the Tretenterates than the annelids. Chronogenesis, though it appears to teil 
equally in favour of Morse’s view, may he held as favourable to the Asteridian 
amnities of the Palliobranchs ; for notwithstanding that Pu latter in a Ramset/ensis 
occurs in a higher horizon of the Cambrian System than the annelids of the Long- 
mynds, Ilicks mentions, in a note appended to bis description of the above species, 
that Torrell and Linnarsson have described forms of a Star-fish from Swedish 
rocks, supposed to he of the Harlech or Longmynd group of the Lower Cambrian. 
Although admitting that the palliobranchs manifest affinities to the annelids, poly- 
zoons, and asterids, I cannot relinquish the idea that they are more closely related to 
the molluscs. If they do not possess sufficiently distinctive characters entitling them 
to rank as a more comprehensive division, I would, instead of associating them with 
any of the first three groups above mentioned, prefer that they retain their old 
Position in the sub-kingdom Mollusca, as defined by Cuvier.” 
I am, however, quite of opinion that, whether the Brachiopods he 
placed in a separate group elose to the Mollusca, or to the Annelids, 
they possess sufficient characters of their own to constitute a well- 
defined dass. 
Distribution in Time. 
Assuming that the reader is acquainted with the geological divi- 
sions into which the crust of this earth has been grouped, I may 
at once observe, as justly remarked by Barrande, in his admirable 
memoir, “ Epreuves des Theories Paleontologiques par la realite,” 
that the Brachiopoda, after the Trilobites, occupy the most important 
place in the Cambrian or Primordial fauna. Thus in 1871, out of 
241 species known to him as composing the animal kingdom of that 
period, 179 are referable to the Trilobites and other Crustaceans, 28 
to the Brachiopoda, while 34 species would be divided between the 
Annelides, Pteropodes, Gasteropoda, Bryozoa, Cystidians, and Spon- 
gida. Subsequent to these researches several additional species of 
Trilobites and Brachiopoda have been added to the list through the 
indefatigable exertious of Prof. Linnarsson, Mr. Hicks, and others. 
If therefore we exclude the problematical <: Eozoon Canadense” from 
the animal creation, as some naturalists have done, 1 we find the 
Brachiopoda along with the groups mentioned by Barrande as the 
earliest representatives of life at present known ; for Mr. Hicks has 
obtained undoubted examples of Lingula or Lingulella ( L . primceva) 
from the very base of the whole Cambrian series of St. Davids in 
Wales. 
It is impossible, for the present, to offer more than an approximate 
comparison, based on numbers, of the genera and species that have 
existed during the various and more or less extended geological, 
periods ; and many years will have to pass away before some master 
minds will be able to grapple with the accumulated observations of 
a Century or more, and reduce the number of genera and species 
within reasonable limits, from which sometking like trustworthy data 
may be formed. Much, indeed, of the confusion must be attributed 
to the imperfection of the information still existing on zoology and 
1 Dawson, Carpenter, Rupert Jones, and others, consider Eozoon to he a 
Rhizopod or Foraminifer ; while King, Rowney, Carter, and others, firmly maintain 
that it is a mineral production. 
