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749 



TERTIARY FAUNA OF FLORIDA 



Pecten (Plagioctenium) eboreus Conrad. 



/'v/<7/ </'<>;<//. Conr., Am. Journ. Sci., xxiii., p. 341, 1833 ; Fos. Med. Teit., p. 48, pi. 



xxiii., fig. 2, and xxiv., fig. 3, 1840. 



/?(/<// t'ici-naiiits Conr., Proc. Acad. Nat. Sci. Phila., i., p. 306, 1843. (Immature shell.) 

 /'trti-n //()//';<'(>/// kavenel, Proc. Acad. Nat. Sci., ii., p. 96, 1844. 

 ? Pt-ctt-n microfili'ura H. C. Lea, Trans. Am. I'hil. Soc., ix., p. 245, pi. 35, fig. 32, 1846. 



(Young shell.) 

 I't'i'li'ii coinpari/is Tuomey and Holmes, Pleioc. Fos. S. Car., p. 29, pi. 11, figs. 6 10, 



I55- 



I't'cti-n yerkcnsis Conr. , Am. Journ. Conch., iii., p. 189-90, 1867. 



j','t /,/! s<i/iin'(i!(/,-s Hcilprin, Trans. Wagner Inst., i., pp. 99, 103, 1887. 



Fossil in the Miocene of Virginia near Suffolk (type), at the north end 

 of the Dismal Swamp, at Snow Hill, at City Point, at Petersburg, in Prince 

 George County, etc.; of North Carolina at Wilmington, and in Duplin 

 County, near and at the Natural Well; of South Carolina at Darlington 

 {comparUis] and Smith's on Goose Creek; and at Alum Bluff and De Land, 

 Florida. Also in the Pliocene of South Carolina on the Waccamaw River 

 (Johnson) and in the Caloosahatchie marls of Florida on Shell Creek and the 

 Caloosa River; Willcox and Dall. 



Pecten microplatra Lea may be the young of P. marylandicus Wagner, 

 rather than of eboreus. It is an immature shell, as is vice narius ; neither has 

 assumed adult characters. 



The rise and progress of this type affords an interesting paleontologic 

 study. 



The young always have the ribs clean cut and squarely channelled and 

 more or less rectangular in section. They also usually have more ribs than 

 the adult, as some one or two on the border of the submargins are apt to 

 become obsolete with growth, though distinct in the young. 



The usual phases noted under /'. gibbiis (of which this form is a pre- 

 cursor) are equally characteristic of eboreus. In the adult the ribs may be 

 low or high, rounded or squarish, with the concentric sculpture equally strong 

 over the whole surface or obsolete on the backs of the ribs, the lamella: feeble 

 and distinct or close and prominent, or the surface sculpture may be almost 

 wholly obsolete. The right valve usually shows one more rib than the left. 

 The radial sculpture on the cars and submargins varies in strength. An 

 examination of eighty-seven specimens resulted in showing that one had 

 seventeen ribs, one eighteen, two nineteen, four twenty, fourteen twenty-one, 

 nineteen twenty-two, eighteen twenty-three, fifteen twenty-four, seven twenty- 



