TRANSACTIONS OF WAGNER 

 746 



TERTIARY FAUNA OF FLORIDA 



Since the original description of Linne was based on Jamaican specimens 

 figured by Browne,* there can be no question as to the proper application of 

 the specific name. The matter has been confused (in spite of Linne's state- 

 ment that the ribs are smooth) by the inclusion of a distinct form with striated 

 ribs figured by Born and Chemnitz and identified by Hanley with P. gibbus, 

 but more recently described by Fischer from Guadelupe, under the name of 

 P. Schrammi. It is true that there are occasional microscopic radial striae on 

 the ribs of P.-dis/ocatns or gibbus, but these do not amount to the strong 

 striation indicated by the figures of Sovverby and Fischer. The specific name 

 gibbus, being the oldest, must be adopted for the species. Its identity was 

 recognized by both Gould and Stimpson, and cannot be doubted by any one 

 who has the privilege of studying a large geographical series. Several fairly 

 recognizable varieties exist, and for convenience will retain their familiar 

 names. The differences appear to be due partly to habitat and partly to situs. 

 In order to test the range of variation in sculpture, I have counted the ribs 

 on two hundred and thirty-five specimens, carefully segregating the varieties, 

 though, necessarily, there was a marked proportion which might have been 

 referred to either of two varieties with equal propriety. In order that the 

 test might be as exact as practicable, the ribs on the left valve, when both 

 were present, were selected for counting; the ridges marking the borders of 

 the submargins were counted as ribs, the riblets of the submargins were not 

 counted, and no specimens less than twenty millimetres in height were used. 



Pecten gibbus var. dislocatus Say ( = gibbus s. s.). 



Miocene to recent. 



The variety dislocatus should be called variety gibbus, since it is the 

 typical form described by Linne, but I retain in this place the more familiar 

 name for temporary convenience. Its range extends from Cape Hatteras to 

 Cape St. Roque in northeastern Brazil, and probably to the Amazon, and it 

 occurs also, if the dealers' labels can be trusted, on the west coast of Africa. 

 A specimen said to be African is variegated with gray and white, and has 

 twenty ribs ; of one hundred and fifty-one American and Antillean specimens 

 three had eighteen ribs ; thirty-six, nineteen ribs ; fifty-five, twenty ribs ; thirty- 

 two, twenty-one ribs ; ten, twenty-two ribs ; and one, twenty-three ribs. It 

 may be said, therefore, that the normal number of ribs for this variety is from 



* P. Browne, Civil and Nat. Hist. Jamaica, p. 41, pi. 40, fig. 10, 1756. 



