Description of a Trilohite. 133 



margin of the head to the glabella; from this point they pass in a 

 slightly curved direction to a point a little within the posterior lateral 

 angle of the cheeks. Frontal suture passing from the intersection of 

 the facial suture and the anterior margin on one side, upward on the 

 front face of the proboscis to a point about midway the length of the 

 same, where it bends at aright angle and proceeds to the intersection of 

 the facial suture on the other side. Labrum not observed. 



Thorax with thirteen segments, narrowing backward and about one 

 sixth longer than wide ; mesial lobe not a§ wide as the lateral, very 

 prominent and depressed on top, with the segments strongl}" defined 

 and arched forward in the middle and at their ends. Lateral lobes 

 flattened on the inner third, then strongly rounded ofl" until the direction 

 to the lateral margin is nearly at right angles to that in the inner third; 

 pleural slightly curved backward to their outer ends, which are round- 

 ed, compressed, expanded, and provided at their posterior edge with a 

 thickened marginal ridge, which becomes gradually stronger to their 

 junction with the segments of the mesial lobe; each provided with a 

 well-defined longitudinal furrow ; on the inner third, and just anterior 

 to the furrow, there is a rather prominent ridge which is placed be- 

 hind, and usually in contact with, the next succeeding segment. 



Pygidium a little wider than long, and as long as the middle of the 

 cephalic shield, exclusive of the frontal prolongation; a direct posteri- 

 or view shows the outline to be semi-circular or broadly semi-ovate, 

 the base appearing straight; viewed from above it is more or less sub- 

 trigonal; mesial lobe well defined, depressed convex, and extending at 

 least three fourfhs the distance to the posterior margin, showing four 

 segments, and very obscurely a fifth; behind these there is a sub-trian- 

 gular space that is not segmented. Lateral lobes sloping off" very rap- 

 idl}', each with four segments, all of which have a slightly defined longi- 

 tudinal furrow. Lateral and posterior borders with a thick margin, 

 which on the exterior is only conspicuous beneath the last segment of 

 the mesial lobe. 



Dimensions of a medium-sized specimen: entire length, 2.8 inches; 

 length of cephalic shield, inclusive of from:al prolongation, 1.0 inch; 

 width of cephalic shield, 1.9 inches; length of glabella and neck fur- 

 row, from base of snout, .69 inch; width of glabella across posterior 

 lobes, .69 inch; length of snout from base in front to apex, .75 inch; 

 greatest width of thoi-ax (just posterior to the cephalic shield), 1.56 

 inches; length of same, 1.8 inches; greatest width of pygidium, .8 inch; 

 length of same .65 inch. 



The most striking feature of this trilobite is the verj^ remarkable de- 



