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TERTIARY FAUNA OF FLORIDA 



characters are non-existent in the one as much as in the other. Gould prob- 

 ably used the word " margaritacea" to express the lustre often seen on polished 

 porcellanous shells, and the " crenulations" are merely the faint incremental 

 radiations common to all bivalves. The examination of authentic specimens 

 of Gould's species (for which I am indebted to the authorities of Cornell 

 University) enables me to make a positive statement in regard to these facts. 

 The shell is not pearly and the margin is not crenulated in the strict sense of 

 those words. The adductor scar is precisely as figured by Fischer for Prasina 

 borbonica, and I can find no trace of any other scar, though the interior is so 

 polished that this would be hardly visible at any rate if present. 



Julia floridana n. s. 

 PLATE 35, FIGURES i, 2, 3. 



Oligocene marl of the Chipola River, Florida ; Burns. 



Shell small, inflated, smooth, arched above, rounded behind, the base 

 nearly straight; the beaks prominent with a small impressed lunule imme- 

 diately under them; below this lunule the valve projects forward to a rather 

 acute point ; with the exception of the groove for the ligament the hinge-line 

 is perfectly simple without teeth or crenulations of any kind ; the edge of the 

 impressed lunule in the right valve is produced into a lamella which fits behind 

 a less prominent extension of the corresponding margin in the opposite valve ; 

 interior of the valves smooth, with no trace of muscular or other scars; 

 exterior sculptured only by faint incremental lines; inner margin of the valves 

 simple, not crenulated ; shell substance showing no traces of nacreous struc- 

 ture, but rather porcellanous. Alt. 4.5, lat. 6.5, diam. 2 mm. 



This species evidently belongs to the same restricted group as the original 

 Frasina borbonica of Deshayes. The chief difference is that the impressed 

 lunule is smaller and not so deep, and that its margin in the left valve is not 

 elevated into so evident a tubercle. Careful scrutiny of more than twenty 

 valves collected failed to show any satisfactory muscular or pallial scars. 



This is the only species known from American deposits and, as far as I 

 have been able to discover, the only fossil species known of the restricted 

 group from any horizon. 



