Ra^^^xT j~<^^y^^^ 



INTRODUCTION 



STUDY OF THE GENERA OF THE PALEOZOIC BRACHIOPODA. 



I. 



BRACHIOPODA IN ART IC UL AT A. 



Valves inarticulated ; intestine terminating in an anus on one side of the body ; shell 



substance largely phosphatic. 



The foregoing characters bring into association a well defined assemblage of 

 these organisms, but, while generally applicable throughout the group in ex- 

 pressing the fundamental distinctions from the more abundantly developed 

 BRACHIOPODA ArtictjlaTa, there often appear, in forms which cannot be separated 

 from such association, tendencies to transgress these limitations in various 

 directions. For example, articulation of the valves was approached, if not 

 effected, in the linguloid Barroisella, in Spondylobolus, and, perhaps also, in 

 Neobolus and Trimerella. In Crania, according to the determination of 

 JouBiN,* the anus opens in the median line of the body; and in various genera. 

 Crania, Pholidops, Trimerella, etc., there is evidence that the substance of the 

 shell was essentially, or altogether calcareous. 



We have preferred to adopt for this division of the Brachiopods, Professor 

 HuxLEv'sf term, Inarticulata, which has the advantage of euphonj^ and sim- 

 plicity. Other writers have made use of terms with different significations, all 



* See under genus Chania. 



t An Introduction to the Classification of Animals, p. 116. 1S69. 



