PLATE VIII 

 TRIARTHRUS BECKI Green (Pages 205-211) 



Figure 1. — Diagrammatic restoration of second thoracic limb in 

 transverse section of trilobite ; showing gnathobases extending under 

 the axis toward the median line, and the biramous limbsunder the pleura 

 and beyond the carapace. 



Figure 2. — Diagrammatic restoration of anterior pair of pygidial 

 limbs ; showing phyllopodiform structure. 



Figure 3. — Diagrammatic restoration of posterior pair of pygidial 

 limbs ; showing more strongly the primitive phyllopodous structure. 



Figure 4. — Dorsal view of second thoracic leg, with gnathobase. X 12. 



Figures 5, 6, 7. — Dorsal views of tliree 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 part of hypostoma, the metastoma, and 

 one endopodite on the right. X 4- 



Figure 9. — Under side 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 4. 



Figure 11. — Diagram ; showing the cephalic appendages preserved 

 in figures 5, 6, 7, and figure 1, Plate VII. 1, shaft of antennule bearing 

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

 terior antennae ; S, third pair of cephalic limbs, or mandibles ; 4, S, 

 gnathobases of fourth and fifth pairs of cephalic limbs, or maxillfe ; hi/, 

 hypostoma; m, mouth ; met, metastoma; s, setpe. This figure is not in- 

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

 a diagram for convenient reference, combining the characters preserved 

 in the specimens illustrated. 



Figure 12. — Portion of the under side of the head and thorax of 

 Apus. %, hypostoma; i, antennule; ^, posterior antenna; S, mandibles; 

 4, 5, maxillas; 6, maxilliped; 7, first thoracic leg ; 8, 9, basal endites of 

 pliyllopodiform legs. X 3. 



