PLATE XXI. 



(rigures 1-39 by II. P. Whitkikld.) 



hegtaui : A. Uelthyrium. c. Ci-ura. 



D. Delti.iium. s- Median septum. 



t. Teeth. s'. Callosity iii the ilelthyrimn. 



d. Dental plates. x. Crural lidges. 

 j. Canlinal pmcess r. Diiluctor Boara. 



b. Denliil sockets. 



Genus SPIRIFER, Sowerbv. 



Pagre 1. 



Spirifeb Niaoakensis, Coiiiiid. 



A medium sized specimen ; showing the railiate-lineate exterior. 

 The interior of the cardinal portion of a brachial valve ; showing the crural plates. 

 A portion of the interior of the pedicle-valve ; showing the elongate muscular area. 

 The median jwrtion of the cardinal areas of conjoined valves ; showing the delti<Uum, cardinal 

 process and crural plates. X 3. 

 Fig. 25. The surface characters. X •^■ 



Niagai-a group. Lockport, N. ¥. 



Spirifer plicatellus, Liiing. 



Figs. 6-8. Figures of typical specimens of this form ; the fii-st from Sweden, the other fi-om the Island of 

 Gotland. Figui-e 28 is an enlargement of the surface of the latter. 



Spirifer radiatus, Soworby. 



Fig. 6. A small individual with a few low lateral plications. This is, apparently, one of the passage forms 

 between the typical S. plicatdlus and the non-plicate S. radiatus. Distinction between the two 

 forms is not possible among American shells. 

 Niagara g^up. Locality f 

 A partial cast of the interior j showing the diductor scai-s. 

 A cardinal view of a specimen partially retaining the deltidium. 



Niagara group. TVegtem New York. 

 A typical non-plicate adult retaining the deltidium. 

 The interior of the pedicle-valve ; showing teeth and muscular scars. 



The interior of the cardinal portion of the brachial valve ; showing the dental sockets and crural 

 plates. 

 Fig. 26. An enlargement of the surface characters. 



Niagara group. Waldron, iTidiana. 



Spirifer radiatus, Sovverl)y (?). 



Figs. 16, 16. Opposite sides of an internal cast of both valves ; showing the elevated cardinal area, and im- 



pi-essions of the long dental plates in tigure 16. 

 Figs. 17, 18. Two views of a larger internal cast ; showing the elevated area, and faint median ridge on the 



brachial valve. 

 Fig. 14. The interior of a portion of the conjoined valves ; showing a low median septum in the brachial 

 valve. 



Niagara dolomites. Wisconsin. 

 This shell is narrower on the lateral slopes than the more typical forms of 5. radiatiut, and differs 

 from them internally in the presence of the slight median septum in the brachial valve. 



