246 



AtTIXOPTERIA DECUSSATA. Hall. (Fig. 160.) (Pal.X.Y., 

 Vol. V.. Pt. I., p. 111. Pis. XVII.. XVIII.. XX, LXXXIV. ) 



Distinguishing < 'haracters — Extreme obliquity : large size; 

 long, well-defined wing; small ear. defined by a sulcus; regu- 

 lar rounded radii, with smaller ones between, regularly inter- 

 rupted by concentric lamellae ; almost obsolete markings on 

 right valve 



Found in the Encrinal limestone, at Sections 5 and <»: in 

 the Stictopora and Demissa beds, at Section 5; and in the 

 Pleurodictyum beds, and the Calcareous bed above them, in 

 Avery's Ravine. 



Actinopteria boydi. Hall. (Fig. 161.) (Pal. X. Y.. Vol. 

 V., Pt. I., p. 113, Pis. XIX., LXXXIV. i 



Distinguishing Characters— less oblique than preceding; 

 larger, less strongly defined wing: continuous surface stria?. 



Fig. 161. Actinopteria boydi. Left and right valves (from Hall I. 



Found in the Pleurodictyum beds, and the Calcareous bed 

 above: also in the shales below the Nautilus bed, in Avery's 

 Creek and on the Lake Shore ( rare I. 



Genus LEIOPTERIA. Hall 



[Ety. : Leios, smooth ; pteria, <v genus.] 

 (1884 : Pal. N. Y.. Vol. V.. Pt. I., p. xiii.) 



Shell resembling Actinopteria in form, with a large wing, 

 the extremity of which is produced. Kays absent. The liga- 

 mental area is external, and marked by fine, parallel, longi- 

 tudinal stria-. Lateral teeth one or two. oblique, slender. 

 Cavity of the beak partially separated from the anterior end 

 by a short partition or diaphragm. 



