A CARBONIFEROUS BRACHIOPOD 663 



a comparatively deep sinus. In the interior of the dorsal valve, the 

 granules are arranged around the margin of the visceral cavity alone. 

 The septa are very weak when compared to the later forms. 



In the Permian rocks (Ft. Riley limestone) we find that the 

 species has reverted. This form is much smaller, has many granules 

 on the interior, brachial and muscle markings weak, is thin shelled and 

 approaches very nearly in shape to the nepionic stage of C. granulifer 

 and therefore the earlier species of the genus. So far as is known, 

 this is the last of the species of Chonetes in the Mississippi basin 

 (Plate III, Figs. 1-3). 



CONCLUSION 



The writer has endeavored to show that, by taking as a basis a 

 series of Chonetes from the horizon of the Upper Carboniferous, 

 forms corresponding to the different stages may be found in the 

 rocks above and below this. Thus the nepionic stage represents 

 species from the Silurian and Devonian; the neanic and early ephibic 

 species from the Carboniferous; and the later ephibic and gerontic 

 species from the Upper Carboniferous, while the Permian or last form 

 reverts back again in form to the early species. 



EXPLANATION OF PLATES 



Plate I. — Series showing ventral view, Florena shales, at Florena and Grand 

 Summit. 



Plate II. — Rows i, 2, Series showing dorsal view, Florena shales, at Florena; 

 cross-section of Grand Summit specimen; cross-section of Prosser's Neosha 

 specimen. Rows 3, 4, Interior of dorsal valves, Florena shales at Florena. 



Plate III. — i, Ft. Riley Limestone; 2, Ft. Riley Limestone; 3, Ft. Riley 

 Limestone; 4, Ft. Riley, No. 10, top of Neosho; 5, Neosho, Prosser's Collection; 

 6, Neosho, Prosser's Collection; 7, Neosho, Prosser's Collection; 8, No. 6 Crusher 

 Hill, bottom of Neosho; 9, Florena at Grand Summit; 10, Florena at Grand 

 Summit; 11, Florena, Ulrich's Quarries near Manhatten, Kan.; 12, Topeka, 

 at Topeka; 13, Topeka, at Topeka; 14, Oread, University Hill, Lawrence, Kan.; 

 15, Oread, University Hill, Lawrence, Kan.; 16, Oread, University Hill, Law- 

 rence Kan.; 17, Oread, University Hill, Lawrence, Kan. 



Plate IV. — i, 2, 3, 5, 6, 7, 8, specimens from the series shown in Plate I, 

 enlarged X20, to show details of marking ventral vein. 4, hinge area enlarged 

 X3. Florena shales at Florena. 



