PLATE 21 



Page 

 Fig. 1. Chonetes mucronata 124 



1 a. A ventral valve, natural size. 



1 4. An enlargement of fig. 1 a, showing more distinctly tlie cliaractcr of Ilie spines. 



1 c. A profile of the same. This form lias few strong strise npoii tlie surface. 



I d, e. A dorsal view, and an enlargement of the same, fiom anotlier individual. The surface is 



marked by more numerous stria; than the siKJcimens 1 a, 1 b. 

 If, g. A ventral view, and the same enlarged. This one is intermediate in number of strife 



between figs. 1 a and 1 d. The above figures are from siHJcimens from the Marcellus shale. 



Fig. :i. Chonetes setiueba 129 



'2 a, b. The ventral valve, natural size and enlarged. 



Fig. 3. Chonetes koninckiana (cited) 13f) 



3. This figure of a siMJcimen of this si)ecies is given for comparison with the varieties of C. 

 coronata. 



Fig. 4. Chonetes sc itula 130 



4 o, b- Ventral and dorsal views of a specimen, natural size, of the ordinary proportion*. 

 4 c. A ventral valve of a smaller individual. 

 4 d. A profile specimen of fig. 4, it, b. 



4 «. An enlargement of the interior of the ventral valve. 



if. An enlargement of the interior of the dorsal valve. i 



Fig. 5. Chonetes lepida 182 



5 o, ft. 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. 



6 «. An enlargement of the interior of a dorsal valve, from which the cardinal process has been 



broken. 



Fig. 6. Chonetes piTsiLLA 12> 



6 a, ft. A ventral and profile view of a specimen of the ordinary size. 



6 c. A si)ecimen of the .same species, (Vora the Corniferous limestone, .showing an extension 



of the cardinal extremities. 



Figs. 7, 8. Chonetes deflecta 12(1 



7 a, b, e. Ventral, dorsal and profile views of an individual ot 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 dor^l valve of a specimen referred to C. gibboia. 



S b, c. A ventral and profile view of the original of C. gibbosa, the s])cciftc distinction of which 

 is doubtful, as noticed imder C. d^ecta, pp. 126 and 12S. 



