41 6 CRETACEOUS PAIvEONTOLOGY. 



species often occurs in great abundance, but usually, after the 

 solution of the shells in this formation, the soft material in which 

 they were imbedded has been compressed, bringing the impres- 

 sion of the exterior and the surface of the internal casts into con- 

 tact, more or less modifying the characters of both. Occasion- 

 ally, however, the species has been preserved in harder nodules 

 OT harder beds in this formation, in such a manner that the casts 

 have essentially the same characteristics as in the Navesink marl. 

 The Merchantville specimens have never been observed tO' attain 

 so large a size as the species sometimes reaches in the Navesink. 

 There seems to be no valid reason for recognizing A. mortoni 

 Con., as distinct from. A. australis Mort., so that the species has 

 here been referred tO' A. suhaustrailis D'Orb., a name proposed as 

 a substitute for Morton's A. australis which was preoccupied. 

 The species differs from A. hamula especially in the less con- 

 vexity of the valves. 



Formation and locality. — Merchantville clay-marl, near Mat- 

 awan (loi, loo*), near Jamesburg (139, 140, 141), Lenola 

 (163), Merchantville (162); Navesink marl, near Crawfords 

 Corner (126'^), near Walnford (147*, 148^, 149, 195), near 

 Jacobstown (150), near Mount Laurel (166) ; Tinton beds, Tin- 

 ton Falls (no), Beers Hill cut, south of Keyport (129^, 129'^, 

 129^), near Freehold (132). 



Geographic distribution. — New Jersey, Alabama, Mississippi, 

 Texas. 



Axinea microdentus n. sp. 

 Plate XXXV., Figs. lo-ii. 



Description. — Shell subcircular, attaining a length and breadth 

 of 21.5 mm. each in the largest specimen observed, the convexity 

 of each valve from one-fourth to three-tenths the diameter. The 

 internal casts somewhat compressed about the free margins, the 

 njargiri very faintly or not at all crenate. Beaks moderately ele- 

 vated, pointed, and slightly oblique, their lateral slopes meeting 

 at an agle of about 90°; the impression of the ' hinge^plate of 

 moderate width, with 11 or 12 teeth on each side O'f the beak, 

 with several less distinct ones in the middle beneath the beak; 



