PLATE XXI II 



RILOBITES ACUTILOBUS Kingukukrg (Page 400) 



FiGUHK 1. Outline of specimen from Niagara (iroup, Lockport, 

 New York. X 4. 



RTLOr.ITKS VERNEUILIANUS LiNDsruiiM (Page 400) 



Figure 2. — Common elongate form from Upper Silurian, (lotland, 

 Sweden. X 4. 



BTLOBITES VARIOUS Conrai. (Pacies 402-405) 



Figures. — Dorsal view of youngest individual observed; sliowing 

 inception of radiating strise and concealment of hinge-areas, x 18. 



Figure 4. — Profile of same; sliowing depth and extent of both 

 valves. X 18. 



Figure 5. — Hinge view of preceding. X 1^. 



Figure 0. — Dorsal side of specimen ; showing Ix^ginuing of anterior 

 marginal sinus, x 18. 



Figure 7. — Profile of same, x 18. 



Figure 8. — Posterior view of same. X 18. 



Figure 0. — Dorsal view of specimen, figure l-") ; showing conceal- 

 ment of ventral area. X 9. 



Figure 10. — Ventral view of same; showing dorsal area. X 9. Com- 

 pare this with dorsal view of larger specimen, figure 21, in series. 



Figures 11-26. — Series of specimens; seen from dorsal side; exhib- 

 itin<i- observed stages of growth, variation and development of hinge, 

 hinge-area, and marginal sinns. X 4. 



Figure 27. —Interior of ventral valve; showing teeth, muscular im- 

 pressions, minute concave plate in apex of fissure, and arrangement of 

 punctaj between nodes and ribs. X 6. 



Lower Ilelderberg Group, Albany county, New York. 



lULOBITHS lilLOBUS Linne (Page 400) 



Figure 28. —Outline; showing characteristic form of this species as 

 occurring in Upper Silurian of Gotland, Sweden. 



