PLATE IV—Continued. 
Schizambon (?) .fissus, Kutorga. 
Fig-. 31. A pedicle-valve; showing- the external character of the aperture. After .Kutorga, op. cit., pi. 
vii, fig. §»/). X 2.5. 
Schizambon (?) fissus, var. Canadensis, Ami. 
Fig. 32. A brachial valve from which the shell is partially broken ; showing the impression of an internal 
median septum. All the spines have been removed except those at and near the margins. 
These have been pressed together in one plane, giving them the appearance of being more 
closely set than when standing at their normal angle upon the surface. X 2. 
Fig. 33. The pedicle-valve ; showing the external character of the pedicle-passage. X 2, 
Fig. 34. A pedicle-valve from which most of the shell has been broken, giving a cross-section of the 
sipho near its inner extremity. X 2. 
Fig. 35. A brachial valve, the correlate of fig. 34. The surface retains most of the shell, but the spines 
are broken, showing only their bases, except at the margins where a portion of their length is 
retained. X 2. 
Fig. 36. A pedicle-valve, so broken as to show the inner edge of the sipho. 
All the above specimens are from the horizon of the Utica slate. Near Gloucester, 
Ontario. 
SlPHONOTRETA (?) MlNNESOTENSIS, Sp. 110V. 
Fig. 37. View from the brachial side of a specimen retaining the valves in juxtaposition and preserving 
most of the epidermal layer of the shell. The spine-bases about the beak are noticeably large 
and more closely set than over the rest of the surface, where they occur at considerable dis¬ 
tances along the concentric varices. The entire length of the spines is evidently not repre¬ 
sented in the fringe about the margin. X 2. 
Fig. 38. The opposite valve of the same specimen. The imperfection of the valve in the umbonal region 
has rendered it impossible to determine with accuracy the generic character of the species. X 2. 
Trenton Limestone. Minneapolis, Minnesota. 
