PLATE 20. 
Page 
Fig. 1. Chonetes mtjcronata.,.. 124 
1 a. Ventral valve of this species; being a small specimen enlarged to two diameters. From the 
Corniferous limestone. 
1 b. Ventral valve of the natural size. From the Corniforous limestone. 
1 c. The specinien fig. 1 b, twice the natural size. 
1 d. The profile of.fig. 1 c. 
Fig. 2. Chonetes mucronata ?. 124 
2. The figure is twice the natural size of the specimen; the plications strong and angular. 
Fig. 8 . Chonetes lineata . 121 
3 a. A ventral valve natural size. 
3 b. The interior of a ventral valve, with a piece of the dorsal valve attached. 
3 c, d. Dorsal and ventral views of specimens twice the natural size. 
3 e. An enlarged figure from the cast of a ventral valve. 
3 /. A section of the two valves. 
Fig. 4. Chonetes yandellana. 128 
4 a, b. Dorsal views of specimens of the natural size. 
4 c. A ventral view of the specimen 4 b. 
4 d. A longitudinal section of the two valves. 
4 e. The specimen fig. 4 a. enlarged to two diameters. 
4/. An enlargement of the interior of a ventral valve. 
4 g. An enlargement of the interior of a dorsal valve. 
Fig. 5. Chonetes acutiradiata. 120 
5 a, b. Ventral views of two individuals, one being much more convex than the other. 
5 c. A profile of fig. 5 a. 
Fig. 6. Chonetes hemispherica. 118 
6 a, b. Ventral views of a small and a large individual. 
6 c. A profile of 6 b. 
6 d. A cardinal view showing the spines upon the margin. 
Fig. 7. Chonetes arcttata. 119 
7 a. A dorsal view of an individual. 
7 b, c. Ventral views of different specimens. 
7 d. A profile of 7 c. 
7 e, f. Ventral and cardinal views of a cast of this species, showing the muscular impression and 
apparently crenulated border caused by the spine-tubes. 
Figs. 8, 9. Strophodonta callosa. 82 
8. The interior of a dorsal valve, taken from a gutta-percha impression. 
9 a. >A cast of the interior of the ventral valve, showing the muscular impression and the thick¬ 
ened border of the valve. 
9 b. A cardinal view of the preceding individual. The figures are all enlarged to two diameter^. 
