PLATE 21 
Page 
Fig. 1. Chonetes mucronata.. 124 
1 a. A ventral valve, natural size. 
1 b. An enlargement of fig. 1 a, showing more distinctly the character of the spines, 
1 c. A profile of the same. This form has few strong striae upon the surface. 
1 d, e. A dorsal view, and an enlargement of the same, from another individual. The surface is 
marked by more numerous striae than the specimens 1 a, 1 b. 
1 f, g. A ventral view, and the same enlarged. This one is intermediate in number of striae 
between figs. 1 a and 1 d. The above figures are from specimens from the Marcellus shale. 
Fig. 2. Chonetes setigera . 129 
2. a, b. The ventral valve, natural size and enlarged. 
Fig. 3. Chonetes koninckiana (cited). 136 
3. This figure of a specimen of this species is given for comparison with the varieties of C. 
coronata. 
Fig. 4. Chonetes scitula . 130 
4 a, b. Ventral and dorsal views of a specimen, natural size, of the ordinary proportions. 
4 c. A ventral valve of a smaller individual. 
4 d. A profile specimen of fig. 4, a, b. 
4 e. An enlargement of the interior of the ventral valve. 
if. An enlargement of the interior of the dorsal valve. 
Fig. 5. Chonetes lepida. 132 
5 a, b- Ventral and dorsal views of a large individual. 
5 c. An enlargement of a ventral valve. 
5 d. An enlargement of the dorsal side, showing the area and spines of the ventral valve. 
5 e. An enlargement of the interior of a dorsal valve, from which the cardinal process has been 
broken. 
Fig. 6. Chonetes pusilla. 128 
6 a, b. A ventral and-profile view of a specimen of the ordinary size. 
6 c. A specimen of the same species, from the Corniferous limestone, showing an extension 
of the cardinal extremities. 
Figs. 7, 8. Chonetes deflecta. 126 
7 a, b, c. Ventral, dorsal and profile views of an individual of the ordinary form and size. 
7 d. A ventral view of an individual which is a little more transverse than the others. 
7 e. An interior of the dorsal valve of the natural size. 
If. An enlargement of the same, showing the muscular impressions, cardinal process, etc. 
7 g. An enlargement of the interior of the ventral valve. 
8 a. The dorsal valve of a specimen referred to C. gibbosa. 
8 b, c. A ventral and profile view of the original of C. gibbosa, the specific distinction of which 
is doubtful, as noticed under C. deflecta, pp. 126 and 128. 
