P LATE 22—Continued. 
Page 
19, 20. Specimens from tlie shales of Eastern Ohio, enlarged to three diameters to correspond 
with the enlargement of the specimen from the Tully limestone. 
21. A specimen of somewhat different, form from the si:rite locality as the last, enlarged to two 
diameters. 
22. A cast from the same locality as the last, enlarged to three diameters, showing the filling of 
the spine tubes in the area. 
24. A ventral view of another individual, showing the spines of the cardinal margin; the curved 
line by the side of the figure shows the convexity of the valve. 
25. The interior of a dorsal valve enlarged to two diameters. These specimens usually pre¬ 
serve the surface marking but obscurely. 
23. A dorsal view, natural size. This, with the two following figures, are from specimens 
from the arenaceous beds below’ the Burlington limestone, at Burlington, Iowa. 
26. A specimen from the oolitic limestone at Burlington, Iowa, in which the surface markings 
are well presei-ved; natural size. 
27. A portion of the surface striae of specimen fig. 26; enlarged to six diameters, for com¬ 
parison with fig. 18. 
28. A portion of the surface enlarged twent}--four times, showing the peculiar undulating rugae. 
igs. 29-43. Chonetes mitricata..... 143 
29,30. Impressions of the exterior of the dorsal valve of this species, one of them showing the 
marks of a few surface spines. 
31, 32. Impressions of the exterior of dorsal valves, with truncated apices, one of them show¬ 
ing the impression of the caidinal process. Both specimens show marks of numerous 
surface spines. 
33. A representation of the interior of the dorsal valve, obtained from an artificial cast of an 
impression left in the stone. 
34, 35. Ventral valves of two individuals, one of them having a truncated beak. Fig. 34 shows 
a few cardinal spines, as usual in Chonetes, w'hile there are numerous smaller ones on the - 
surface. Fig. 35 has a shorter hinge line, with wrinkled ears, which are studded with 
spines as in Productus. 
36, 37, 38. Specimens of the casts of the ventral valves having the features obscurely pre¬ 
served, showing three forms of the shell. 
39. A cast of the ventral valve, with adhering stone, preserving impressions of the cardinal 
spines. 
40. A cast of the ventral valve, showing the marks of the muscular impressions very distinctly. 
41. A cardinal view of the specimen fig. 35. 
42. A cardinal view of the specimen fig. 38. 
43. An enlargement of part of a ventral valve, combining the characters of muscular impres¬ 
sions, etc-, observed in several individuals. 
ig. 44. Chonetes arcttata. 119 
44. A cardinal view, showing the distant Slender spines. From the Corniferous limestone. 
