PLATE 5. 
Page 
Pigs. 1, 2. Orthis lenticularis... 35 
1 a, b. Dorsal and ventral views. 
1 c. Profile of the above. 
1 d, e .. Cardinal and front views of the same shell. 
2 a, b. 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. Orthis propinqua. 43 
3 a, b. Yentral and dorsal views of a small gibbous specimen, from cherty layers of Corniferous 
limestone at Lapham’s mill, Ontario county. 
3 c. Profile of the above. 
3 d, e. Yentral, and dorsal views of a large individual, from near Columbus, Ohio. 
3 f. Profile of the above. 
3 g. A cast of the dorsal valve, showing muscular and vascular impressions; from Avon, N. Y. 
Fig. 4. Orthis livia. 38 
4 a. b. Dorsal and ventral views of a specimen from the Corniferous limestone of Western New 
York. 
4 c. Profile of the.above. 
Fig. 5. Orthis sp. ?. 39 
5 a, b. Dorsal and ventral views of a specimen. 
Fig. 6. Orthis vanuxemi ?. 40 
6 a, b. 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. 0. eryna, see Errata. 
