ARTHROPOD A— INSECT A. 419 



number of genera and species. Examples: Acantherpestes major 

 Meek and Worthen (Fig. 1720) ; Euphoberia armigera Meek and 

 Worthen (Fig. 1722, 7, 8) ; E. granosa Scudder (Fig. 1721) and 

 other species; Amynilispes wortheni Scudder (Fig. 1722, 1-4 and 

 9) ; Eileticus anthracinus Scudder (Fig. 1722, 5, 6). Trichiulus 



Fig. 1723. Xylobim sigillarice. a, natural size ; b, anterior portion, enlarged ; ^, pos- 

 terior portion, enlarged. (After Dawson.) 



villosus Scudder and other species (all from Mazon Creek), and 

 Archiulus xylobioides Scudder, etc., and Xylobius sigillariae Daw- 

 son (Fig. 1723) and other species from the Coal Measures of 

 Joggins, Nova Scotia. 



The Chilopoda are Tertiary and extra American, but the Diplo- 

 poda, which first appear in the Cretacic of Greenland (Julopsis 

 cretacea Heer) are represented in the American Oligocenic by 

 Julus telluster Scudder from the Green River beds of Wyoming, 

 and another species from the 'Make beds" of Florissant Colorado. 



Class INSECTA (Hexapoda, Insects). 



Insects are air-breathing Arthropoda with the body separated 

 into head, thorax, and abdomen, covered by a chitinous exoskele- 

 ton capable of preservation. The hard integument is in reality 

 composed of a number of plates or sclerites connected by delicate 

 membrane, the dividing line being often indicated by sutures. 

 Respiration is by means of air tubes or trachece which penetrate 

 the body and wings. The head consists of four fused segments 

 with a pair of appendages corresponding to each. These are, from 

 before backwards: a single pair of antennce, attached to the main 

 part of the head (epicranium) ; a pair of mandibles, one of niaxil- 

 Ice (anterior maxillae), and the under lip or labiimi (posterior 

 maxilla), the basal segments of the opposite members of which 

 are more or less attached to the clypeus or front sclerite of the 

 head. There is also an upper lip or labrum. Both maxillae and 



