TRANSACTIONS OF WAGNER 

 1244 



^^ TERTIARY FAUNA OF FLORIDA 



subequilateral, with a conspicuous, often caducous, periostracum. The valves 

 close tightly, are usually more or less convex, and are devoid of sculpture 

 though often forcibly colored. The pallial line has a small, wide, short sinus 

 rounded in front. There is on the hinge-margin a single anterior left lateral 

 which is received between two more or less distinctly developed laminae in the 

 opposite valve. Some of the cardinals towards the middle of the series are 

 usually broad and bifid. The left anterior and right posterior margins of the 

 valves, beyond the hinge-plate proper, are more or less distinctly grooved to 

 receive the bevelled edges of the valve opposite. The periostracum in the typical 

 section is peculiar in having, over a polished substratum, a layer of silvery 

 color and velvety texture which is very easily removed by friction and is always 

 absent from beach-worn specimens. 

 The genus is divided as follows : 



Section Tivela s. s. Type Venus mactroides Born. 



Valves trigonal, with smooth interior margins, and a periostracum super- 

 ficially pilose when fresh ; cardinals varying from four to six in either valve in 

 different species. 



Section Pachydesma Conrad. Type Donax stultorum Mawe. 



Shell very large, elongate-trigonal, with smooth interior margins, a vernicose 

 dehiscent periostracum, and four cardinals in each valve. 



Section Eutivela Dall. Type E. perplexa Stearns. 



Shell small, elongate, with crenulate interior margins, thin, polished perios- 

 tracum, three left and four right cardinal teeth. 



The genus DoUfusia Cossmann is placed hereabouts by Fischer, but I have 

 not been able to examine a specimen. It belongs to the Parisian Eocene. 



Tivela jamaicensis n. sp. 

 Plate 57, Figure 9. 

 Oligocene of the Bowden marl at Bowden, Jamaica, rare ; collected by 

 Henderson and Simpson. 



Shell small, thin, pkimp, smooth, or faintly concentrically striated; beaks 

 nearly central, low pointed, turgid ; lunule large, lanceolate, smooth, defined 

 by an impressed line ; nymphs short and elevated, dorsal slopes nearly straight, 

 ends bluntly rounded, base slightly arcuate; hinge delicate with three small 



