224 
externally by numerous longitudinal ribs, chambers 
formed by transverse septa perforated by a tube 
which is either central or marginal. 
O. Lecumen. Lam. 6.—F. p. 237.—Navtitus L. 
Lin. 1164.—D. p. 350.—Gualt. t. 19. f. P.—Turt. 
D. p. 121.—(Walk. t. 3. f. 74. N)—Mont. Sup. p. 
82.¢.19. fi. 6.—Lin. T. 8 p. 118.—White, smooth, 
glossy, transparent, somewhat flattened, a little concave ; 
on one side, without marginal ridge on either side, a 
little curved, slightly tapering or nearly of equal diam- 
eter at both ends, the extremes a little rounded and 
contracted ; joints eight or nine, divided by oblique 
lines, the anterior or larger end oblique and margined, 
with an obtuse syphon which rises above the margin and 
a considerable aperture near the concave side.—Variety, 
N. Rectus. Mont. p. 197. ¢. 19. f. 4,7.—Turt.D. 
p. 121.—Walk. f. 74.—Straight and subcylindrical. -— 
Variety, N. Susarcuatus. Mont. p. 198. ¢. 6./f. 
5.—Turt. D. p. 122.—The three anterior chambers 
more globose than the rest. 0,12 Margate, §c., in fine 
sand, 
O. Costata. F. p. 236.—Navutitus C. Mont. p. 
199. 4.14. f. 5.—D. p. 348.—Turt. D. p. 122— 
Lin. T. 8. p. 120.—Straight, subcylindrical, with from 
five to twelve raised articulations which are adorned 
