PLATE 5. 



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Figs. 1, 2. Orthis lenticclaris 35 



1 a, b. Dorsal and ventral viewa. 

 1 c. Profile of the above. 



1 d, e. Cardinal and front views of the same shell. 



2 a, 6. Dorsal and ventral views of a larger shell. • 

 2 c, d. Profile, and front view of the same. 



2 e. Interior of a ventral valve. 



Fig. 3. Ortiiis PROPINQ0A 43 



3 a, b. Ventral and dorsal views of a small gibbous specimen, from cherty layers of Comiferous 



limestone at Lapham's mill, Ontario county. 

 3 c. Profile of the above. 



3 d, «. Ventral, and dorsal views of a large individual, from near Columbus, Ohio. 

 8/. Profile of the above. 



'& g. A. cast of the dorsal valve, showing muscular and vascular impressions; from Avon, N. Y. 



Fig. 4. Orthis livia 38 



4 o. 6. Dorsal and ventral views of a specimen ft-om the Comiferous limestone of Western New 



York. 



4 c. Profile of the above. 



Fig. 5. Orthis sp. ? 39 



5 a, b. Dorsal ttnd ventral views of a specimen. 



Fig. 6. Orthis vanuxemi ? 40 



6 o, 6. The exterior and interior of a ventral valve. 



Fig. 7. Orthis semele 40 



7. The exterior of a ventral valve, showing the extent of the hinge-line. 



8. The interior of a ventral valve. The specimen occurs in the same stone with fig. 7, but the 



hinge-line is imperfect and does not appear to have been so much extended as in that 

 specimen. 



Figs. 9, 10. Orthis cleobis 41 



9. A cast of the dorsal valve, showing the impression of the area. 



10. A cast of the ventral valve. 



Fig. 11. Orthis idas 42 



11 a, b. Dorsal and ventral views of the same specimen. O. eryna, see Errata. 



