498 s. weller mississippian rhynchonelliform shells 



Introduction 



Among all the Paleozoic brachiopods no type of shell configuration has 

 greater range, greater distribution, or greater representation than the 

 rhynchonelliform shells, and previous to the appearance of the great 

 work on the Genera of Paleozoic Brachiopoda, by Hall and Clarke,^ the 

 more common custom was to refer all these shells to the genus Bhyn- 

 chonella. It was pointed out by these authors, however, that the geno- 

 type of Bhynchonella, B. loxia Fischer, from the Upper Jurassic fauna 

 of Eussia, was, in its assemblage of external and internal characters, 

 clearly distinct, generically, from any of our Paleozoic forms. They 

 recognized, furthermore, no less than sixteen generic or subgeneric groups 

 of rhynchonelliform shells in the Paleozoic faunas, to which either new 

 names were given or for which previously published names were revived. 

 No attempt was made by these authors to distribute all the species of 

 Paleozoic Ehynchonelloids in their proper genera, but in his "Synopsis 

 of American Fossil Brachiopoda'^ Schuchert^ has attempted to so dis- 

 tribute the species so far as was possible. More than a hundred species, 

 however, were allowed by Schuchert to remain in the genus Bhynchonella, 

 because their internal characters had never been investigated and it was 

 impossible to place them properly without such an investigation. 



The present study is an attempt to determine the essential generic 

 characters of some of the rhynchonelliform shells of the Mississippian 

 faunas of the Mississippi Valley basin. The method of study has been 

 to grind down the shells from the beak toward the front, on a carborum- 

 dum wheel, the surface being polished and careful cross-section drawings 

 being made at frequent intervals. From the drawings of these serial 

 sections the internal arrangement of the septa and other lamelliform 

 plates, the hinge-plate, crura, spondylia, and cruralia can be interpreted 

 with ease. The investigation has been extended to include certain rhyn- 

 chonelliform shells which have been referred to the Pentamerid genus 

 Camarophoria by Hall and Clarke and by Schuchert, all of which were 

 originally described as members of the genus Bhynchonella. 



Camarophoria King* 



CAMAROPHORIA SCHLOTHEIMI {VON BUGH) 



At the outset of the investigation it is important to determine the 

 essential differences between Bhynchonella, used in its broad sense, and 



8 Paleontology of New York, vol. viii, parts 1 and 2 (1891-1894). 

 3 Bulletin of the U. S. Geological Survey, No. 87 (1897). 

 * fSuperfamily Pentameracea Schuchert. 



