PLATE IV— Cou tinned. 



ScHizAMBON (?) Fissus, Kutorga. 



Fig-. 31. A pedicle-valve ; showing the external chai'acter of the aperture. After Kdtorga, op. cit., pi. 

 vii, fig. 5a'). X 2.5. 



SCHIZAMBON (?) FISSUS, VJIV. CANADENSIS, Ami. 



Pig', 'i'l. A brachial valve from which tlie sliell is partially broken ; showing the impi'ession of an internal 

 median septum. All the spines have been removed except those at and near the mai-gins. 

 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 extei-nal charactei- of the pedicle-iiassage. 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 con-elate 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 hoi'izon of the Utica slate. Near Q-loucester, 

 Ontario. 



SiPHONOTRETA (?) MiNNESOTENSIS, Sp. IIOV. 



Fig. 37. View from the brachial side of a sfiecimen retaining the valves in juxtajjosition and i^reserving 

 most of the epidermal layer of the shell. The spine-bases about the beak are noticeably la]-ge 

 and more closely set than over the rest of the sui-face, where they occui- at considei-able dis- 

 tances along the concenti-ic varices. The entire length of the spines is evidently not rejire- 

 sented in the fi-inge about the margin. X 2. 



Fig. 88. The opposite valve of the same specimen. The imperfection of the valve in the umlional region 

 has rendered it impossible to determine with accuracy the generic character of the species. X 2. 

 Trenton Limestone. Minneafiolis, Mim,nesota. 



