28 PLATE XIII. [Assembly 



1 



Shells of the Hamilton group. i 



BRACHIOPODA. 



1. Strophomena tnequistriata. 



2. Spirifer zigzag. 



3. Atrypa reticularis (p. 67). 



4. Spirifer mucronatus, lower valve (p. 67). 

 6. Same, front view. 



6. Same, shorter variety. 



7. Same, very elongated variety. 



8. Atrypa aspera. 



9. Same, front view. 



10. Same, magnified portion of surface. 



11. Same, with the spines still adhering in parts. 



12. Atrypa concinna. 



13. A. concentrica, lower valve (p. 67). 



14. Same, front view. 



15. DiSCINA GRANDIS (p. 67). 



