Eocene and Vioksbui', j , ?rom the II, -oristiphora Dall and Sinip- 

 son fl), the recent representative of the group in the V/est 



(1). Bull. U. S. Pish Oonm., vol. 20, "ot . 1, p. 495, ^^1. 55, 

 figs. 4, 5, 1901. 



Indies, it di"^"" ""- by its more quadrEite-elongate form, thinner 

 shell, and more delicate and sparser ooncentrie lamellae." 

 (Ball, 1905). 



'?^:-pe_ looalitv .- Boi^rien, Jsrcaica. 



The anterior dorsal marp-in ort, straight or slightly 



excavate:', direct or with a ^ ' . slope and aoru-otly Joining 

 tlie ohliquely suhtrinic ated upoer anterior lateral margin; while 

 the posterior dorsal marrin is longer, direct or slightly; con- 

 vex and passes ahruptlj' into the vertically tnmcated posterior 

 end. 



Her!sr"'rs .- This species is quite abundant in the material 

 at hand, the largest valve measaring 11.9 niri. in latitude, 11 mm. 

 in altitude and 2.2 inm. in diameter. Variation in inflation is 

 displayed, some of the valves heinr more than moderately convex. 

 There are also contrasts in the concentric sciz!J.pture , vrhich ranges 



from hTit slightly elevaterl lamellae to much more consnicuox^s lam- 

 ellar fring-es; m.uch of this is, however, due to erosion. The 



lamellae are always sharp atid closely siaaced. Some valves from 



