PLATE n— Continued. 



OBOLELLA, Billings. 



Page 6G. 



Obolella crassa, Hall. 



Fig. 31. The exterior of a valve. Natural size. 



Pig'. 82. The same, enlai-g-ed ; showing- the radiating striae between the laniellose growth-lines. X 2. 



Fig. 33. Another valve, similai-ly enlarged, in whicVi the radiating lines do not appear. This is the speci- 

 men originally described as Avicida desquainata. Hall (Pal. N. Y., vol. i. 1847). 



Fig. 34. The interioi' of a pedicle-valve ; showing the pedicle-g'roove, the cardinal, lateral and centi'al mus- 

 cular scars. X 2. 



Fig. 35. The interior of another, but smaller, pedicle-valve : showing the same features. X 2. 



Fig. 36. The intei-ior of the Vjrachial A'alve ; showing the faint pedicle-groove, the cardinal, external, cen- 

 tral and lateral muscular impressions. X 2. 



Middle Cambrian. Near Troy, N. Y. 



Obolella polita, Hall. 

 Fig. 37. The extei-ior of a valve. X 4. 



Fig. 38. The interior of a pedicle-valve ; showing the centi-al and lateral muscular impressions. X 2. 

 Fig. 39. An internal cast of the opposite (1) valve. X 2. 

 Fig. 40. The interior of a brachial valve X 6. 

 Fig. 41. The interior of a pedicle-valve. X 6. 



(Figs. 40 and 41 are from the original drawings represented in the Sixteenth Rept. N. Y. State 

 Cab. Nat. Hist., pi. vi. figs. 20, 21.) 



Potsdam sandstone. Trempaleau, Wisconsin. 



Obolella gemma, Billings. 



Fig. 42. The exterior of a pedicle-valve. X 6. 



Fig. 43. (34 in error, last line of figTires.) The interior of a brachial valve ; showing the muscular im- 

 pressions. X 6. 



Fig. 44. The interior of a pedicle-valve ; showing the cardinal area, pedicle-groove and muscular im- 

 pressions. X 6. 

 (The oi-iginals of figs. 1, 2, 4, 34, 35, 36, 42, 43, 44, are in the collection of Mr. S. W. Ford.) 



