LAMELLIBRANCHIATA OF THE LOWER MARLS. 53 



Left valve smooth or but faintly marked by fine concentric lines, and a 

 few (five or six) very faint radii. Ears smaller than in the opposite valve, 

 both sloping toward the beak on the onter margin. Right valve mai-ked 

 with crowded concentric folds or elevated lines ; also by five or six radiat- 

 ing lines; not always present. On most specimens thei'e are distinctly 

 rounded concentric folds or varices, but on some they are thin, sharp lines; 

 always more crowded and usually finer toward the front, in adult specimens. 

 Ears very distinct; that of the posterior side sloping toward the beak and 

 the anterior one rounded at the extremity and deeply notched. 



This shell is very closely allied to P. simplicus, Conrad, but differs in 

 being more elevated and in the surface markings, that one being generally 

 smooth or imperceptibly marked. In making these comparisons I have 

 used a number of each valve of the present species from New Jersey, and a 

 fine series of A. simplicum from the typical locality, Eufaula, Ala., and it 

 leaves no doubt in my mind as to their complete specific distinction. 



Formation and locality. — In the fine blue clay marl of the Lower Green 

 Sand at Haddonfield, New Jersey. The specimens are from the collection 

 of the Academy of Natural Science, Philadelphia, and being borrowed I 

 have not attempted to examine the hinge structure, as they are so very 

 fragile that the least disturbance of the matrix might result in the destruc- 

 tion of the shells. 



Camptonectes (Amusium) Burliiigtonensis. 

 Plate VIII, Figs. 3-9. 



Pecteti Burlingtonensis, Gabb. J. A. N. Sci., Phil., 2d .ser., Vol. IV, p. 304, PI. LXVIII, 



Fig-. 25. Syuops. p. 157. Meek, Check-list, p. 7. 

 Sincyclonema Burlingtonensis (Gabb). Meek, Geol. Surv. N. J., 1868, p. 725. 

 Camptonectes Burlingtonensis (Gabb). Conrad, Am. J. Couch., Vol. VI, p. 76. Gabb, 



P. A. N. Sci., 1876, p. 318. 

 C. helUsculptus Conrad. Am. Jour. Conch., Vol. V, p. 99, PL IX, Fig. 11. 



Shell attaining a full medium size, one specimen measuring two and a 

 half inches in height, and is equally wide, being nearly circular exclusive 

 of the auriculations. Hinge-line straight, not more than half as long as 

 the width of the shell; ears moderately large. Valves convex, cardinal 

 slopes of the body of the shell concave in their course from the beak, the 



