PLATE XIII. 

 LixGULOPS^ Whitfieldi Hall. 



Page 245. 

 Fig. 1. View of a ventral valve enlarged six diameters, showing the general char- 

 acters of the external surface. 

 " 3. A partial cast of a ventral valve, showing the arrangement of some of the 

 muscular and parietal scars, and also the ramifications of the vascular 

 lines, which, although originating at nearly the same points as in recent 

 Lingulae, do not extend so far backward toward the beak. 



DlGNOMIA ALVEATA Hall. 

 Page 245. 

 Fig. 8. View of a cast of a ventral valve, showing the impression of the longitudinal 

 septum along the center of the valve. Hamilton group, New York. 



LiNGULELLA DaVISII Salt. 

 Page 245. 

 Fig. 4. Interior of a ventral valve, enlarged : after Mr. Davidson. 



LiNGVLELLA AURORA VAR. Hall. 

 Page 245. 

 Fig. 5. Impression of the interior of a ventral valve enlarged, showing the extent of 

 the area and the form of the deltidial opening. Potsdam Sandstone, Wis 



DICELL03IUS CRASS A Hall. 



[Obolella (pars) Billings.] 

 Page 246. 

 Fig. 6. External view of the smaller valve. 

 " 7. Internal cast of the same valve, showing the widely diverging muscular 



impressions. 

 " 8. Exterior of the larger valve. 



" 9. Internal cast of the same valve, showing the character of the muscular 

 imprints. (Figures all enlarged two diameters.) 



Rhys OB ol us 9 



[Compare Oboltjs galtexsis Billings.'] 

 Page 247. 

 Fig. 10. View of the interior of a ventral valve as obtained from a gutta-percha 

 mold of the natural cast of the interior, showing the general characters 

 of the shell. From the Guelph Limestone, Gait, Ont., Can. 



TrIMERELLA GRAXDIS Bill. 

 Page 247. 

 Fig. 11. Interior of a dorsal (?) valve as obtained from a gutta-percha mold taken 

 from the original specimen used by Mr. Billings. Loaned by A. R. C. 

 Selwyn, director of the Geological Survey of Canada. 

 " 12. A transverse section across the middle of the valve, showing the form of 

 the elevated muscular plate and the cavities beneath. 



♦Printed Ligolops by mistake in some copies of the paper. 



