Plate I. 



All figures are of Pentremites sulcatus and are from photographs of speci- 

 mens in the author's collection: enlarged two diameters. 



1. An ambulacrum, showing a sigmoid flexure in the ambulacral integu- 

 ment. 



2. Summit view, showing distortion of the openings caused by lateral 

 pressure. 



3. An ambulacrum, showing an extensive mechanical injury. 



4. An ambulacrum, showing destruction and subsequent restoration of 

 the apex. 



5. Showing an injury in the upper third and the subsequent healing, and 

 the loss of the poral pieces on the opposite side. 



6. Scar of mechanical injuries on both sides of the field. 



7. A similar injury, on one side of the field. 



