TRANSACTIONS OF WAGNER 



TERTIARY FAUNA OF FLORIDA 



of ribs varies from twenty-six in the roundest, A. Holincsii, to thirty-five in 

 the most elongated, A. amcricana ; but the short, round ones often have as 

 many ribs as the elongated specimens. The cardinal area is extremely narrow 

 and depressed, and the portion in front of the beaks is very small. The ante- 

 rior granular series of teeth is much shorter than in A. tolcpia, and does not 

 extend much in front of the beaks. 



The species does not descend below the uppermost Miocene, if, indeed, any 

 of the specimens are so old. I have only identified it with certainty from the 

 Pleistocene of Georgia, of Simmons Bluff, South Carolina, of New Jersey, and 

 southern New England. 



Section JlafJiynrca Kobelt. 



Scapharca (Bathyarca) Spenceri n. s. 

 PLATE 32, FIGURES 16, 24. 



Pliocene of Tehuantepec ; Dr. J. W. Spencer. 



Shell large for the section, inflated, ovate, with prominent prosocoelous 

 beaks; left valve with fine, rounded, concentric elevated lines, close set, and 

 with very narrow interspaces, which show fine, close radial striae, some of 

 which on the anterior end of the shell are more prominent ; right valve with 

 fine, close-set radial ribs, coarser on the middle of the shell, separated by 

 narrower, sharp, channelled grooves ; transverse sculpture of evenly spaced, 

 low, sharp elevated lines which cross the ribs without becoming much 

 thickened ; cardinal area very narrow behind, wider but not distinctly limited 

 in front, the cardinal margin elevated anteriorly, with seven or eight con- 

 centric grooves mostly behind the umbones ; ends of the hinge angular 

 behind ; the teeth in two series hardly separated, eight to twelve in front, 

 ten to fourteen behind, not crowded, smaller mesially, larger and more oblique 

 distally, the anterior series somewhat irregular; inner margin of the valves 

 with fine crenulations, stronger in the left valve, the outer edge almost or 

 quite entire. Lon. 18, alt. 15, diam. 14 mm. 



This is the largest species of the section, and was collected by Dr. J. W. 

 Spencer about seventy kilometres west of the eastern terminus of the Tehu- 

 antepec Railway from a cutting, together with a number of otiier species, all 

 of which indicated that they were deposited in deep water, probably between 

 one hundred and fifty and four hundred fathoms in depth, judging by analo- 

 gous recent species The matrix is a fine, soft, grayish mud like that of deep- 

 water deposits of the same kind, and its presence with the fossils points to 

 a Post-Pliocene elevation of this part of the land of at least one thousand 



