• PLATE 20. 



Page 



Fig. 1. Chonetes muceonata 124 



1 a. Ventral valve of this species; being a small specimen enlarged to two diameters. From the 



Corniferous limestone. 

 1 6. Ventral valve of the natural size. From the Gorniforous limestone. 

 1 c. The specimen fig. 1 b, twice the natural size. 

 1 d. The profile of fig. 1 c 



Fig. 2. Chonetes muceonata ? 124 



2. The flgare is twice the natural size of the specimen; the plications strong and angular. 



Fig. 3. Chonetes lineata 121 



8 o. A ventral valve natural size. 



8 b. The interior of a ventral valve, with a piece of the dorsal valve attached. 



8 c, d. Dorsal and ventral views of specimens twice the natural size. 



8 e. An enlarged figure from the cast of a ventral valve. 

 if. A section of the two valves. 



Fig. 4. Chonetes tandellana 123 



4 a, 6. 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 



6 a, b- Ventral views of two individuals, one being much more convex than the other. 

 6 c. A profile of fig. 5 a. 



Fig. 6. Chonetes hemispheric a 118 



6 a, b. Ventral views of a small and a large individual. 

 6 c. A profile of 6 6. 



6 d. A cardinal view showing the spines upon the margin. 



Fig. 7. Chonetes arcuata 119 



7 a. A dorsal view of an individual. 



7 b, e. Ventral views of difi"erent specimens. 

 7 d. A profile of 7 c. 



7 «,/. 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 o. A cast of the interior of the ventral valve, showing the muscular impression and the thick- 



ened border of the valve. 

 9 ft. A cardinal view of the preceding individual . The figures are all enlarged to two diameters. 



