CHAPTER XVIII 



PALAEONTOLOGY OF THE BRACHIOPODA 



INTKODUCTIOX DIVISION I. ECARDINES EXTERNAL CHAR- 

 ACTERS — INTEPvNAL CHARACTERS DIVISION II. TESTI- 



CARDLNES — EXTERNAL CHARACTERS — INTERNAL CHAR- 

 ACTERS — SYNOPSIS OF FAMILIES — STRATIGRAPHICAL 

 DISTRIBUTION — PHYLOGENY AND ONTOGENY 



Introduction 



Th £, wide distribution and vast abundance of the Brachiopoda 

 throughout the whole series of geological formations make this 

 group of especial importance to the student of the past history 

 of the earth; and the zoologist must always regard the fossil 

 forms with peculiar interest, because they not only largely out- 

 number the living representatives, but comprise numerous extinct 

 genera, and even families, exhibiting types of structure and char- 

 acters entirely absent in the modern members of the group. 

 It is a most fortunate circumstance that the excellent state of 

 preservation in which we frequently find them, and the immense 

 amount of material at our disposal, enable us to determine with 

 accuracy and certainty the internal characters of the shells in 

 the great majority of cases. But it is only since the beginning of 

 the present century that our knowledge of the anatomy of the soft 

 parts of the living animal has rendered any tracing of homologies 

 possible. In the case of features in fossil extinct types the inter- 

 pretation must be to some extent doubtful. Barrande, Clarke, 

 Davidson, Hall, King, Oehlert, Waagen, de Verneuil, and a host 

 of other workers have contributed to the information which we 

 now possess ; and their works must be consulted for details of the 

 subject.^ 



1 J. Barrande, Syst. Silur. Boheme, vol. v., 1879. Hall and Clarke, Introd. 

 Palaeozoic. Brack. {Palaeont. of New York, 1892-1894). Davidson, Monogr. 



491 



