﻿T. Davidson — What is a Brachiopod? 267 



dating 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 tell 

 equally in favour of Morse's view, may he held as favourable to the Asteridian 

 affinities of the Palliobranchs ; for notwithstanding that Falasterina Eamset/ensis 

 occurs in a higher horizon of the Cambrian system than the annelids of the Long- 

 mynds, Hicks mentions, in a note appended to his description of the above species, 

 that Torrell and Linnarsson have described forms of a Star-fish irom 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 Molhcsca, as defined by Cuvier." 



I am, howevei', quite of opinion that, whether the Brachiopods he 

 placed in a separate group close to the Mollusca, or to the Annelids, 

 they possess sufficient characters of their own to constitute a well- 

 defined class. 



Destkibhtion 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 exertions of Prof. Linnarsson, Mi'. Hicks, and others. 

 If therefore we exclude the problematical "Eozoon Canadense" from 

 the animal creation, as some naturalists have done,^ 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 something 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 



* Dawson, Carpenter, Eupert Jones, and others, consider Eoznon to be a 

 Rhizopod or Foraminifer ; while King, Eowney, Carter, and others, firmly maintain 

 that it is a mineral production. 



