PLATE XIII. 



Page. 

 Idonearca vulgaris Morton , 98 



Fig. 1. Lateral view of a cast of the usual form of the species. 



2. Anterior profile view of the same. 



3. Lateral view of a cast of an old and thickened specimen. 



4. Cardinal view of the same. 



5. View of a cast of a single valve, showing the outline of the shell aud teeth. 

 Idonearca antrosa Morton 96 



Fig. 6. Lateral view of a cast of medium size. 



7. Anterior profile view of the same. 



8. Lateral view of another, larger but imperfect cast. 



9. Anterior profile view of the same. 



10. View of the exterior of a specimen from the limestone nodules from Holmdel, N. J. 



This is the form described by Mr. Gabb as./, neglecta. 



11. View of a cast which retains the shell on one valve partially showing the teeth, 



which are represented on the posterior side as obtained from a gutta-perclia 

 cast in the shell of the opposite valve. 



294 



