Maryland Geological Survey 541 



? Axincca subaustralis Conrad, 1868, Cook's Geol. of New Jersey, p. 725. 

 Axincca mortoni Conrad, 1869, Am. Jour, of Conch., vol. v, p. 44, pi. i, fig. 14. 

 ? Axincca subaustralis Gabb, 1876, Proc. Acad. Nat Sci., Phila., p. 317. 

 Axinea mortoni Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 99, pi. 



xi, figs. 23-25 (ex parte). 

 Axinea alta Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 101, pi. xi, 



figs. 26-29. 

 Pectunculus australis Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 10. 

 Axinea subaustralis Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, 



p. 414, pi. xxxv, figs. 1-8. (Synonymy excluded.) 



Description.- — " Suborbicular, nearly equilateral, convex; beaks small, 

 pointed, slightly prominent, central ; inner margins crenulated." — Morton, 

 1834. 



Type Locality. — Prairie Bluff, Alabama. 



" Shell subcircular in outline, varying in size from 15 mm. to 40 mm. 

 in diameter, the convexity of each valve being from one-fourth to three- 

 tenths the diameter; very slightly oblique, the beaks central in position. 

 The internal casts compressed about the free margin especially in adult 

 shells, the margin strongly crenulate when well preserved. The beaks 

 strongly elevated and pointed, their lateral slopes meeting in an angle 

 varying several degrees either way from 90° ; the impression of the hinge- 

 plate broad and arcuate, with nine or ten strong teeth on each side of the 

 beak, directed at nearly right angles to the inner margin of the hinge- 

 plate, and with several smaller teeth in the middle beneath the beak. 

 Anterior and posterior muscular impressions well denned, especially in 

 the larger specimens. The shell substance thick, marked externally with 

 more or less irregular, concentric lines of growth, and by regular radiating 

 costae which are more or less interrupted by the concentric lines upon 

 partially exfoliated individuals. The beaks approximate and the cardinal 

 areas small with divergent furrows." — Weller, 1907. 



The species is represented, in both the Matawan and the Monmouth of 



Maryland, only by imperfect casts. When the dorsal margins are broken 



away, as they frequently are, the contour of the remainder suggests a 



quarter circle. The umbones are small, compressed, acutely pointed, and 



35 



