698 THE PALEONTOLOGY OF MINNESOTA. 



[.Terminology. 



The pi/;/i(linm, P, consists of a number of anchylosed segments, their parts on 

 the axis being known as annulations, an, and on the pleura 1 as ribs, pr. The ribs may 

 terminate within the margin of the shield or be produced beyond it. The extremity 

 of the pygidium may be obtuse, angular or continued into a caudal spine, cs. 



The test of all the parts is continued beyond and beneath the margin, the enfolded 

 portion or doublure extending but a short distance inward. This is trans-sected by 

 the anterior limbs of the facial suture, or by a branch or branches from those limbs. 

 That portion of the doublure lying beneath the anterior extremity of the head and 

 sometimes isolated by the sutures is the epistoma. Below this lies a free subquadrate 

 or subtriangular plate, the hypostoma. The doublure is more or less distinctly 

 developed at the extremities of the thoracic segments and within the margin of the 

 pygidium. 



