212 THE CHICAGO ACADEMY OF SCIENCES. 



Lateral Pertaining to or proceeding from the side. 



Lateral furrows The transverse furrows or grooves of the trilobite 

 glabella, sometimes continuous across the glabella and sometimes 

 greatly modified. 



Limb of pygidium The lateral areas of the trilobite pygidium exclusive 

 of the axis. 



Marginal border The thickened or otherwise differentiated external 

 border of the cephalon and pygidium of the trilobites. 



Marginal furrow The groove or depression lying just within the mar- 

 ginal border of the cephalon and pygidium of the trilobites. 



Neck segment The occipital segment. 



Ocelli The simple eyes present upon the fixed cheeks of some trilo- 

 bites. 



Occipital furrow The posterior transverse groove or furrow of the 

 glabella of trilobites, lying in front of the occipital segment. 



Occipital lobes Small, lateral lobes of the occipital segment present in 

 some trilobites, which are morphologically different from the lateral 

 lobes of the glabella. 



Occipital segment The posterior transverse segment of the trilobite 

 glabella, lying between the posterior margin and the occipital fur- 

 row. 



Ocular ridges Ridges extending from near the anterior extremity of the 

 glabella to the eyes in some trilobites. 



Ontogeny The life history of an individual organism. 



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

 the eyes. The eye lobes. 



Plurae The two lateral longitudinal lobes of the trilobite, applied 

 ' chiefly to the thoracic region and the pygidium. 



Post axial region The flattened area occupying the median portion of 

 the pygidium of some trilobites, posterior to the elevated axis. 



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



Posterior Situated behind. 



Posterior cheek furrow The marginal furrows or grooves present in 

 some trilobites, which extend across the cheeks from the extremi- 

 ties of the occipital furrow of the glabella towards the genal angles. 



Posterior limb of facial suture That portion of the facial suture ex- 

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

 lateral margin of the cephalon. 



Protaspis The earliest recognized stage in the development of the trilo- 

 bite test. 



Protopodite The basal portion of the typical crustacean appendage 

 whieh^supports distally the exopodite and the endopodite. 



Proximal Towards the center. 



Pygidium The tail or posterior region of the trilobite test. 



Schizochroal eyes Compound eyes of the trilobites in which the visual 

 area is occupied by small openings for the separate facets. 



Test Thejhard outer covering of the trilobite. 



Thorax The central segmented region of the body of the trilobite. 



Ventral Pertaining to the under surface. 



