TRANSACTIONS OF WAGNER 

 648 



TERTIARY FAUNA OH FLORIDA 



This species is easily recognized by its numerous oblique ribs and com- 

 pressed posterior end. 



Scapharca (Scapharca) acompsa n. s. 

 PLATE 33, FIGURK 15. 



Oligocene of the Chipola River, Florida, marl. 



Shell rectangular, elongate, rather compressed, with low prosoccelotis 

 beaks, situated at about the anterior fourth of the whole length ; right valve 

 with about thirty-six flattened radial ribs, with much narrower interspaces ; 

 the anterior (twenty-two) ribs are mesially divided by a sharp groove and 

 feebly rippled above ; the posterior ribs are flat, smooth, and increase in width 

 backward ; the anterior end of the shell is evenly rounded, the base straight 

 and parallel with the hinge-line, the posterior end wider, a little produced 

 below and with a conspicuous angle above ; cardinal area long, very narrow, 

 with one or two grooves, and bordered behind with an elevated margin ; 

 hinge-line straight, long, with numerous small, uninterrupted teeth very short 

 mesially, longer and somewhat more oblique distally ; inner margin of the 

 valves fluted, shell thin and delicate. Lon. 20, alt. 10.5, semi-diam. 4.5 mm. 



Only two right valves of this little species have been examined. It 

 resembles the young of A. liypomcla but is immediately distinguishable by its 

 more compressed and rectangular form and smooth, flat posterior ribs. 



Scapharca (Scapharca) triphera n. s. 

 PLATE 33, FIGURK 6. 



Pliocene marls of the Caloosahatchie River, Florida ; Dall. 



Shell subequivalve, of moderate size, elongate, not much inflated, sub- 

 rectangular, with low beaks slightly prosoccelous and marked by a conspicuous 

 wide mesial sulcation ; umbones situated at the anterior third of the length ; 

 left valve with about thirty-eight rounded subequal ribs separated by narrower 

 interspaces ; in the adult about a do/en of the anterior ribs may be squared 

 off and deeply mesially sulcate near the margin, while a few of the ribs on 

 the posterior dorsal slope are narrower, smoother, and more widely separated; 

 transverse sculpture of elevated lines which are somewhat regularly spaced, 

 and in crossing the ribs develop into sharp, thick transverse nodulations ; 

 cardinal area very narrow and with an elevated margin behind, slightly wider 

 in front of the beaks, longitudinally striate ; ends of the hinge-line angular; 

 anterior end bluntly rounded, base parallel with the hinge-line, posterior end 



