24 North American Palaeozoic Crustacea. 



simple linear hinge; the two extremities of the hinge-border form 

 angles with the anterior and posterior borders of each valve. The 

 right valve larger than the left, being broader and overlapping com- 

 pletely the ventral border of the opposite valve, and to some extent its 

 anterior and posterior borders. This overlap forms a thick blunt keel 

 to the closed carapace. Rather above and in front of the centre of 

 each valve, and on its most convex portion there is a raised, circular, 

 or suboval swelling ; on the interior surface of the valve this is marked 

 by a corresponding pit. Type L. Britannica, Rouault. 

 Cytherina alia, Conrad, 1842; Geol. Kept. New York, 3d Geol. Dist. (Vanuxem), 

 p. 112. Lower Helderberg. 



Cytherina alta? Hall, 1852 ; Pal. New York, vol. 2, p. 338, pi. 78, figs. 2a-d ; 



referred to Leperdilia Jonesi, Hall ; id., vol. 3, p. 372. 

 Leperditia alta, Jones, 1856; Annals & Mag. Nat. Hist., 2d series, London, 

 vol. 17, p. 88, pi. 7, figs. 6, 7. 

 alta, Jones, 1858 ; Annals & Mag. Nat. Hist., 3d series, London, vol. 1, 



p. 250, pi. 10, figs. 10, 11. 

 alta, Hall, 1859; Pal. New York, vol. 3, p. 373, pi. 79 a, figs. 6a-e. 

 alta, Meek, 1873; Pal. Ohio, vol. 1, p. 187, pi. 17, figs. 2a, b. 

 alta, Jones, 1881 ; Annals & Mag. Nat. Hist., 5th series, London, vol. 8, 



p. 346. 

 alta, Whitfield, 1882 ; Geol. Wisconsin, vol. 4, p. 323. pi. 25, fig. 8-9. 

 alta, Jones, 1884; Annals & Mag. Nat. Hist., 5th series, London, vol. 14, 



p. 343. 

 amygdalina, Jones, 1858; Annals & Mag. Nat. Hist., 3d series, London, 

 vol. 1, p. 341. Trenton, 



amygdalina, Jones, 1858 ; Geol. Survey Canada, Dec. 3, p. 97, pi. 11, 



figs. 18, 19. 

 amygdalina, Jones, 1881 ; Annals & Mag. Nat. Hist., 5th series, London, 



vol. 8, p. 344, pi. 19, fig. 9. 

 amygdalina, Jones, 1884; id., 5th series, London, vol. 14, p. 342. 

 angulifera, Whitfield, 1881 ; Annals New York Acad. Sci., vol. 2, p. 199. 



Lower Helderberg. 

 Anna, Jones, 1858; Annals & Mag. Nat. Hist., 3d series, London, vol. 1, 

 p. 347, pi. 9, fig. 18. Calciferous. 



Anna, Jones, 1858 ; Geol. Survey Canada, Dec. 3, p. 96, pi. 11, fig. 13, 

 Anticostiana, Jones, 1884; Annals & Mag. Nat. Hist., 5th series, London, 

 vol. 14, p. 241. Hudson River. 



Canadensis, var. Anticostiana, Jones, 1858; Annals & Mag. Nat. Hist., 



3d series, London, vol. 1, p. 341. 

 Canadensis, var. Anticostiana, Jones, 1858; Geol. Survey Canada, Dec. 3, 



p. 95, pi. 11, fig. 17. 

 Anticostiana, Billings, 1866 ; Catalogue Sil. Fossils Anticosti, p. 68. 

 fubulites (Conrad), var. Anticostiana, Jones, 1881 ; Annals & Mag. Nat. 



Hist., 5th series, London, vol. 8, p. 344, pi. 19, fig. 8. 

 arctica, Jones, 1856; Annals & Mag. Nat. Hist., 2d series, London, vol. 17, 

 p. 87, pi. 7, figs. 1-5. Upper Silurian. 



