P LATE 22— Continned. 



Page 

 19, 20. Specimens fixni tlic f-liales of Eas^tcm Ohio, enlarged to three dismeters to correspond 

 with the enlargtment of the specimen from tlie Tully limestone. 



21. A specimen of somewhat difJerenl, form ft-cm the sime 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 hpine tubes in the area. 



24. A ventral view of another individual, showing the spines of tlie 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, natuisl size. This, with the two following figures, are from specimens 



from the arenaceous beds below the Burlington limestone, at Burlington, Iowa. 



26. A sp<'cimen from the oolitic lime.»ti.ne at Burlington, Iowa, in which the surface markings 



are well preserved; natural size. 



27. A portion of the surface stria; of specimen fig. 26; enlarged to six diameters, for com- 



parison with fig. 18. 



28. A portion of the surface enlarged twenty-four times, showing the peculiar undulating ruga;. 



Figs. 29-43. CUONETES MURICATA 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, 82. Impressions of the exterior of dorsal valves, with truncated apices, one of them show- 

 ing the impression of the catdinal process. Both specimens show marks of numerous 

 surface spines. 



33. A representation of the interior of the dorsal valve, obtained from an artilioial cast of an 



impression left in the stone. 



34, 36. Ventral valves of two indiuduals, one of them having a truncated beak. Fig. 34 shows 



a few cardinal spines, as usual in Chonetes, while there are numerous smaller ones on the 

 surface. I'ig. 85 has a shorter hinge line, with wrinkled ears, which are studded with 

 spines as in Pruductut. 

 36, 87, 38. Specimens of tlie casts of the ventral valves having the features obscurely pre- 

 served, showing three forms of the shell. 



39. A ca.st of the venlral valve, witli 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 8i)ecimen fig. 35. 



42. A cardinal view of the specimen fig. 88. 



43. An (Milargomcnt of part of a. ventral valve, combining the characters of muscular impres- 



sions, etc., observed in several individuals. 



Fig. 44. Chonetes aecuata 119 



44. A cardinal view, shmving the distant slender spines. From the Cornifcrous limestone. 



