54 
BULLETIN OF THE LABORATORIES 
IL Axial lobe of glabella expanded anteriorly. 
(a) of medium size. 
f. pigidium rather longer than wide. 
3. F. eichwaldi^ Fischer. Head nearly semi-circular, eyes large. 
3a. P. eichwaldt^ var. 7 nucronata, McCoy. Pigidium, with a me- 
dian posterior prominence. (Plate VI, 8.) 
4. P. leei^ Woodward. Eyes very small. 
X. pigidium broader than long. 
5. S. cliffordi^ Woodward. Pigidium twice as wide as long. 
(b) . Of small size. 
6. P. minor ^ Woodward. 
B. Angle of free cheeks not produced to form a conspicuous 
spine. 
I. Anterior margin of glabella not expanded. 
7. P. derbiensis, Martin, (Plate VI, Fig. 12.) 
II. Anterior margin of glabella expanded. 
a. Pigidium wider than long. 
8. P. colei^ McCoy, (Plate VI, Fig. ii.) 
b. Pigidium longer than wide. 
9. P. scabra, Woodward. 
Known only from pigidia. 
10. P. articulosa^ Woodward. Resembles P. cliffordi, differing 
in having seventeen coalesced somites instead of thirteen. - 
11. P carinata^ Salter. Axis of the tail acutely ridged, seven- 
teen segments. 
12. P. laticaiidata, Woodward. Pigidium very wide, with 
twelve somites, axis elevated. 
American Species. 
Known from both heads and pigidia. 
.1. P. swallovi, Shumard. 
, 2. P. shumardi\ Herrick. 
, 3. P. sagainonensis , Meek and Worthen. 
« 4. P. scitula^ Meek and Worthen. 
. 5. doris, Winchell. 
'6. P. rockfordensis, Winchell. 
» 7. P. insignis^ Winchell. 
8. P. irimuleata, Herrick. 
