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I 300 



TERTIARY FAUNA OF FLORIDA 



ribbing from any of the other species of the genus, recalling in this respect 

 some of the forms of Chione. It has so far been obtained only from the lower 

 or Chipolan bed at Alum Bluff, where it is rather abundant. 



Venus Ducateli Conrad. 



Venus Ducateli Conrad, Fos. Medial Tert., p. 8, pi. iv., fig. 2, 1838 ; Proc. Acad. Nat. Sci. 

 Phila., xiv., p. 574, 1863 ; Whitfield, Mioc. Moll. N. Jersey, p. 67, pi. xi., figs, i, 2, 3 

 (only), 1895. 



Miocene of Cumberland County, New Jersey, and near Church Hill, Mary- 

 land ; Harris. 



This species differs from V. mercenaria by having solid, thick, elevated 

 ribs, more or less recurved, and expanded and more elevated after they pass 

 upon the posterior dorsal area. The corrugated area of the hinge is rela- 

 tively small compared with that of V . mercenaria, which is probably the reason 

 why Conrad left the species in Venus while putting the allied forms in Mer- 

 cenaria in 1863. Mr. Whitfield very properly called attention to the fact that 

 V '. Ducateli was congeneric with V . mercenaria. However, part of the decorti- 

 cated material which he doubtingly included under this name, and which is 

 represented by his figures 4, 5, 6, and 7, belongs to another species, V. plena. 



Venus plena Conrad. 

 Mercenaria plena Conrad, Am. Journ. Conch., v., p. 100, 1869; Whitfield, Mioc. Moll. N. 



Jersey, p. 69, pi. xii., figs. 4-6, 1895. 



Venus Ducateli Whitfield (ex parte), op. cit., pi. xi., figs. 4-7, 1895. 

 Venus plena Heilprin, Proc. Acad. Nat. Sci. Phila. for 1887, pp. 397 and 403. 



Older Miocene of Cumberland County, New Jersey, at Shiloh and Jericho ; 

 of Plum Point, Maryland ; Miocene of Virginia on the York River, near Belle- 

 field and Yorktown, and of North Carolina at Wilmington. 



This is a small but often quite thick and heavy species, of which the most 

 abundant mutation found near Yorktown is a flattish oval shell which suggests 

 a dwarf V. Rileyi, but which passes into a thinner and more inflated form, such 

 as those figured by Whitfield from New Jersey. The maximum length which 

 I have noted among the specimens in the National Museum is seventy-five 

 millimetres. The shell has a much smaller rugose area on the hinge than is 

 found in V. mercenaria of the same size. When the sculpture is intact, which 

 rarely occurs, it exhibits close-set, thickish, rather low concentric lamellae. 

 None show any smooth medial area or thickened ribs, except when part of the 

 surface is deficient. In outline the species passes through much such a series 



