CRUSTACEANS. 227 



Illaenus insignis? Hall. 

 riate xxxii, Qgs. la-b. 



lUcenus insignis Hall, 1S64 : Advance sheets New York State Cab. Nat. 



Hist., 20th Kept, p. 27. 

 Illcenus insignis Hall, 1808 : New York State Cab. Nat. Hist., 20th Rept. 



p. 331, pi. xxii, figs. 13-14. 

 Illcenus insignis Meek, 1873: Geol. Sur. Ohio, False., vol. I, p. 189, pi. xv, 



figs. 5a-c. 

 Illcenus insigtiis Whitfield, 1882: Geol. Sur. Wisconsin, vol. iV, p. 305, 



pi. xxi, figs. 6-10. 

 Illcenus insignis Foerste, 1886; Geol. and Nat. Hist. Sur. Minnesota, 15th 



Ann. Kept., p. 481. 



Large, elliptical. Cephalic shield moderately convex, 

 widest behind the middle ; posterior margin nearly straight ; 

 marginal border narrow. Glabella rather strongly convex; 

 dorsal sinuses well defined. Facial sutures extending forward 

 from each eye with a distinct outward curve. Movable cheeks 

 sloping off rapidly on each side. Eyes large. Pygidium con- 

 siderably larger than head-piece. Surface smooth. 



Horizon! and localities. — Upper Silurian, Niagara ? lime- 

 stone : Pike and St. Louis counties. 



Acidaspis hamata? (Conrad). 

 Discranurus hamata Conrad, 1841 : 5th Ann. Rep. N. Y. Geol. Sur., p. 48, 



pl. l,fig.l. 

 Discranurus hamata Hall, 1862: TSth Rep. N. Y. State Cab. Nat. Hist., 



pl. ii, fig. 1. 

 Acidaspis hamata Hall, 1859: Pal. New Y'ork, vol. Ill, p. 371, pl. Ixxix, 



figs. 15-19. 

 Acidaspis hamata Meek & Worthen, 1868: Geol. Sur. Illinois, vol. Ill, p. 



290, pl. vii, fig. 17. 



Only fragmentary remains supposed to be closely related to, 

 if not identical with Conrad's species are known from Missouri. 



Horizon and localities. — Upper Silurian limestone : Bailey's 

 Landing (Perry county). 



