PLATE VIII 

 TRIARTIIUUS BECKI Grken (Pages 205-211) 



FiGUHK 1. — Diagrammatic restoration of second thoracic limb in 

 transverse section of trilobite; sliowing gnatliobascs extending iinder 

 the axis toward the median line, and the biramous limbs under the pleura 

 and beyond the carapace. 



FiGUUE 2. — Diagrammatic restoration of anterior ]iair of ji^'gidial 

 limbs ; sliowing phyllopodiforin structure. 



FiGUKE 3. — Diagrammatic restoration of posterior pair of pygidial 

 limbs ; showing more strongly the primitive phyllopodous structure. 



Figure 4.— Dorsal view of second thoi'acic leg, with gnathobase. X 12. 



Figures 5, 6, 7. — Dorsal views of three heads; showing antennules. 

 Their position in figure 7 is the most common. 



Figure 8. — Portion of under side of head ; showing plate-like gnatho- 

 bases of cephalic limbs, posterior jiart of hypostoma, the metastoma, and 

 one endopodite on the riglit. X 4. 



Figure 9. — Underside of head, with gnathobases and metastoma 

 better preserved. X 4. 



Figure 10. — Under side of head; showing antennules and their 

 points of attachment, the four pairs of gnathobases of the other cephalic 

 limbs, and the hypostoma and metastoma in the median line. X l- 



FiGUUE 11. — Diagram; showing the cephalic ap]iendages preserved 

 in figures .'), 6, 7, and figure 1, Plate VII. 1, shaft of antennule bearing 

 a single flagcllum ; 2, coxopodite of first pair of biramous limbs, or pos- 

 terior antenna); 3, third pair of cephalic limbs, or mandibles; Jf., 5, 

 gnathobases of fourth and fifth pairs of cephalic limbs, or maxilla^; %, 

 hypostoma; m, mouth; j?ie<, metastoma; .?, setne. This figure is not in- 

 tended as a complete restoration of the cejihalic appendages, but only as 

 a diagram for convenient reference, combining the chaiacters preserved 

 in the specimens illustrated. 



Figure 12. — Portion of the under sid<' of the head and (borax of 

 Ajms. %, hypostoma ; 2, antennule; i?, posterior antenna ; 5, mandibles; 

 Jf, 5, maxilla^; 6, maxilliped; 7, first thoracic leg ; S, 0, basal endites of 

 phyllopodiform legs. X 3. 



