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I 22Q 

 TERTIARY FAUNA OF FLORIDA 



obsolete, becoming lamellar laterally; pallia"! sinus short, angular, horizontally 

 directed; lateral tooth smooth, feeble; middle left and two posterior right 

 cardinals bifid; right posterior margin beyond the hinge-plate grooved to 

 receive the edge of the opposite valve. 



In the young the edges of the valves adjacent to the ligament pout more or 

 less obviously, a character lost or obscure in the adult. 



Section Dosinisca Dall, 1902. Type Artemis alata Reeve. 



Areas of the lunule and escutcheon pouting mesially, defined by a pro- 

 nounced sulcus, forming a posterior wing which recalls Phacoides; sculpture 

 of fine, rather distant, sharp lamellae, sometimes with radial striation; valves 

 thin ; pallial sinus deep and angular ; lateral tooth entire. 



This group is distributed in Australia and Japan. 



Section Dosinidia Dall, 1902. Type Venus concentrica Born. America. 



Valves suborbicular, more or less compressed, white, with a sculpture of 

 concentric grooving, the interspaces never lamellose ; furnished with an obvious 

 periostracum ; lunule small, impressed ; escutcheon absent ; pallial sinus ample, 

 ascending, angular in front; middle cardinals broad, sulcate or bifid, anterior 

 lateral small, feeble, smooth. 



This group is confined to the tropical and warmer temperate waters of 

 America, where it replaces all the other sections of the genus. The nepionic 

 young have the, posterior cardinals corrugated and there are obscure traces of a 

 posterior lateral, but these characteristics are soon lost and leave no traces in 

 the adult. 



Dosinia (Dosinidia) chipolana n. sp. 

 PLATE 54, FIGURE 4. 



Oligocene of the Chipola horizon on the Chipola River, Calhoun County, 

 Florida, at Alum Bluff and the silex beds at Ballast Point, Tampa Bay. 



Shell rather small and thin, suborbicular, moderately convex, with full, 

 pointed beaks, with fine, sharp concentric grooves having the distal side more 

 abrupt, the interspaces flattish and hardly raised towards the ends of the shell ; 

 lunule lanceolate, impressed; beaks sculptured like the rest of the shell; an- 

 terior dorsal margin convexly arched; hinge-plate rather short and wide; 

 teeth normal; the adductor scars large; the pallial sinus ample, ascending, 

 acute in front, terminating two-thirds the distance forward from the posterior 

 to the anterior adductor. Height 37.5, length 40.0, diameter 17,0 mm ? 



