TRILOBITES. 709 
Ptychopyge ulrichi.] 
Subgenus PTYCHOPYGE, Angelin, 1854. 
PTYCHOPYGE ULRICHI, 7”. sp. 
This species is represented in the material before me by seven more or less com- 
plete pygidia; one small and entire, 21 mm. in length and 35 mm. in greatest width; 
another, a part of a very large one, fully 120 mm. in width across the top. The general 
form of the first is semi-oval except about the margins which are broadly concave. 
Fig. 12.—An entire pygidium of Ptychopyge ulrichi, Cannon Falls. : 
The lobation is clearly defined, the axis being relatively narrow, slightly more than 
one-fifth the entire length of the shield, and extending for somewhat more than 
two-thirds the length of the pygidium, ending in a blunt, not elevated extremity. 
z Fig. 13—Fragment of a large pygidium of Ptychopyge ulrichi, with restoration of outline. Cannon 
Falls. 
It bears eight or nine annulations, only the first three or four being well defined. 
The pleurz are convex and rather short on account of the broad, concave margin. 
Besides the articulating segment there are five ribs, with a trace of a sixth; and on 
the internal cast seven or eight ribs may be discerned. Of these the first is the 
