46 Field Museum of Natural History — Geology, Vol. IV. 



Occipital or neck segment: The posterior transverse segment of the 

 trilobite glabella, lying between the posterior margin and the occipital 

 furrow. (3) 



Ocular ridges: Ridges extending from near the anterior extremity of 

 the glabella to the eyes in some trilobites. The eye lines. 



Palpebral lobes: Lobes of the fixed cheeks within the margins of 

 the eyes. The eye lobes. (18) 



Pleura: The two lateral longitudinal lobes of a trilobite, applied 

 chiefly to the thoracic region and the pygidium. (p) 



Pleural grooves: Grooves on the pleura? of the thoracic segments. 



(14) 



Pleural ribs: The fused segments in the lateral lobes of the pygidium. 



(10) 



•Post-axial region: The flattened area occupying the median portion 

 of the pygidium of some trilobites, posterior to the elevated axis. (11) 



Post-cephalic margin: The posterior margin of the head or cephalon. 



Posterior cheek furrow: The marginal furrows or grooves present in 

 some trilobites, which extend across the cheeks from the extremities of 

 the occipital furrow of the glabella towards the genal angles. (8) 



Posterior limb of facial suture: That portion of the facial suture 

 extending from the posterior extremity of the eye to the posterior or 

 lateral margin of the cephalon. (6) 



Proximal: Toward the median line. 



Punctate: Having minute depressions or pits. 



Pustulose: Covered with pustules or blister-like prominences. 



Pygidium: The tail or posterior region of the trilobite test. (P) 



Schizochroal eyes: Compound eyes of the trilobites in which the 

 visual area is occupied by small openings for the separate facets. 



Segments: The transverse divisions of the thorax or pygidium. 



Test: The hard outer covering of the trilobite. 



Thorax: The central segmented region of the body of trilobites. 

 (T) 



Ventral: Pertaining to the under surface. 



