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TERTIARY FAUNA OF FLORIDA 



This is a remarkable species first named in 1818 by Lamarck from a patho- 

 logical mutation figured by Lister, and renamed by Say six years later. The 

 normal and healthy form of the species was not named until 1838, when Con- 

 rad called it V. Rileyi, while his last name, V. percrassa, was given to a par- 

 ticular form of the pathological monstrosity. It is impossible to determine 

 the precise cause of the deformity and hypertrophy of the peculiar individuals. 

 Such have been found from the York River, Virginia, to Darlington, South 

 Carolina, though the normal form, V. Rileyi, has a much wider range. I have 

 seen a few specimens of V. Mortoni and V. mercenaria similarly affected, and 

 in recent shells the access of an excess of fresh water sometimes produces simi- 

 lar abnormal characters. However, V. tridacnoides seems to have been pecu- 

 liarly liable to this deformity. The species may be divided as follows : 



Venus tridacnoides Lamarck : 



A. Variety tridacnoides s. s. 



This includes deform is Say and percrassa Conrad. 



B. Variety Rileyi Conrad. 

 This is the normal form of the species. 



The shell from the Post-Pliocene beds at Heislerville may perhaps be a 

 mutation of V. mercenaria towards the Rileyi type. If this be eliminated, the 

 species may be regarded as restricted to the Miocene and Pliocene, being com- 

 paratively rare in the beds of the later age. 



Venus mercenaria Linn^ 

 <^J''enus mercenaria Linne, Syst. Nat, ed. x., p. 686, 1758; Fauna Suecica. p. 519, 1761 ; 



Syst. Nat., ed. xii., p. 1131, 1767; Gmelin, Syst. Nat., vi., p. 3271, 1792; Dillwyn, Cat. 



Rec. Sh., i., p. 176, 1817 (cf. Lister, Hist. Conch., pi. cclxxi., fig. 107, 1692). 

 Venus mercenaria Spengler, Schrift, Berl. Ges. Naturf. Freunde, vi., p. 307, pi. vi., figs. 



I, 2, 3, 1785; Cliemnitz, Conch. Cab., x., p. 352, pi. clxxi., figs. 1659, 1660, 1788; 



Lamarck, Prodrome, p. 84, 1799; An. s. Vert., v., p. 591, 1818; Akerly, Am. Monthly 



Mag., ii., p. 296, 1818; Say, Journ. Acad. Nat. Sci. Phila., ii., p. 271, 1822; Wood, Ind. 



Test., p. 35, pi. vii., fig. 40, 1825; Mitchill, Am. Journ. Sci., ist Sen, x., p. 287, 1826; 



Conrad, Journ. Acad. Nat. Sci. Phila., vi., p. 209, 1830 ; Greene, Mass. Cat., 1833 ; 



Gould, Inv. Mass., p. 85, fig. 67. 1841 ; Deshayes. Enc. Meth. Vers., iii., p. 1117, pi. 



cclxxiii., 1832; Lamarck, An. s. Vert., ed. ii., vi., p. 346, 1835; Mighels, Boston Journ. 



Nat. Hist., iv., p. 320, 1843; Stimpson, Shells of N. Eng., p. 19, 1851 ; Sowerby, Thes. 



Conch., ii., p. 733, pi. clxii., figs. 204-^06, 1853 ; De Kay, Zool. of New York, v., p. 217, 



pi. xxvii., fig. 276, 1843 ; Reeve, Conch. Icon., xiv., Mon. Venus, pi. ii., fig. 46, 1863 ; 



