BRACHIOPODA. 217 



the second division is referred the shell described by Geinitz,* from the Upper 

 Carboniferous or Permian of Nebraska, as Rhynchonella angulata, Linne. Ac- 

 cording to Meek and Waagen, the Carboniferous species, Terebratula Andii and 

 T. Gaudriji, of d'Orbigny, from Bolivia, are to be referred to Enteletes. 



Future study of the species of Orthis which have not been accessible during 

 the preparation of this work, will no doubt necessitate the establishment of 

 still other groups of equivalent value to those here proposed ; but there will, 

 of course, always remain forms of intermediate structure which can not be in- 

 cluded in any strict classification. It is, however, gratifying to find relatively 

 so few species which can not be placed under the foregoing subdivisions. 



There is a small group of shells exemplified by such forms as Orthis punctata, 

 de Verneuil, from Gotland, and 0. pmdostriata, Hall, from the Niagara fauna, 

 which have a true orthoid interior but a peculiar external form, and a surface 

 covered by radiating rows of circular superficial punctae, very similar to those 

 marking the genus Porambonites. Other species for which it is difficult to find 

 a place in this grouping are a few of the type of 0. Bouchardi, Davidson, 0. 

 Nisis, Hall, and 0. rugiplicata, Hall. The early species which have been refer- 

 red to Orthis require especially careful consideration. From later study of 

 the species described by Mr. Billings, from the Quebec group, examples of which 

 have been kindly furnished by the Directors of the Geological Survey of Canada, 

 and of the Redpath Museum of Montreal, it is shown that one of them, 0. 

 gemmicula, must be removed to another genus; another, 0. apkalis, is very 

 doubtfully an Orthis ; while 0. Mijcale and 0. Tritonia appear to have no cardi- 

 nal process in the brachial valves; 0. Hippohjte, which in external features 

 might be classed with the punctate group of 0. testudinaria, is an impunctate 

 shell. The species 0. Armanda and 0. Corinna have a leptsenoid form, and 

 their relations are evidently quite remote from typical Orthis. These species 



* Carton, and Dyas in Nebraska, p. 37, pi. iii, figs. 1-4. Mr. Meek regarded this as identical with 

 Enteletes hemiplicatus (Report Palfeontology of Eastern Nebraska, p. 178. 1872) 



