FREE INSTITUTE OF SCIENCE 

 TERTIARY FAUNA OF FLORIDA 



run the whole shell, ribs, and interspaces, and at short intervals, at the inter- 

 section with the inner pair of rib-threads, they become minutely nodulous, 

 while the reticulations have a punctate appearance, giving a surface somewhat 

 like fine lace and peculiar, as far as observed, to this species ; cardinal area 

 short, rather narrow, with sharply elevated boundaries and a single incised set 

 of grooves forming a lozenge-shaped figure anteriorly ; hinge-line short, teeth 

 in two adjacent series, anterior with fifteen, posterior with twenty-six or 

 twenty-seven teeth set vertically, a little oblique at the distal ends of the 

 series ; each individual tooth more or less grooved or striate in the direction 

 of motion, as in some recent species ; anterior end of shell produced, 

 rounded ; posterior end subtruncate, base slightly arched ; inner margin of 

 the valves with rather long, deep flutings, corresponding to the external ribs. 

 Lon. 32, alt. 27, diam. 20 mm. (twice the diameter of the single valve). 



A single valve of this very elegant species was obtained by Mr. Burns. 

 Its sculpture differentiates it from all our other Tertiary species. Area calli- 

 filcnra Conrad, in which the ribs have a minute nodular sculpture, has the 

 radial threading predominant, while in this species the concentric threads over- 

 run all the rest. The two species are entirely distinct otherwise. 



Scapharca (Scapharca) idonea Conrad. 

 .hrti idoiii-a Conrad, Fos. Tert. Form., p. 16, pi. I, fig. 5, 1832. 

 Area stillicitiiiiin Conrad, op. fit., p. 15, pi. I, fig. 5 (young shell). 

 Ai'tti itlenca Conrad, Fos. Med. Tert., p. 55, pi. 29, fig. 3, 1840. 

 Sni/i/itirri! iilonea Conrad, I 'roc. Arad. Nat. Sci. Phila. for 1862, p. 579, 1863. 



The typical form has twenty-five ribs, and has been obtained from the 

 Miocene of St. Mary's River, Maryland, and the upper bed at Alum Bluff, 

 Florida. The more elongated variety, with thirty-one ribs, figured in the 

 Medial Tertiary, is also found at St. Mary's, at Windmill Point, and in Surry 

 County, Virginia, and in the Miocene of Alum Bluff, Florida. A somewhat 

 more angular type than either of the above is obtained from the Miocene of 

 St. Mary's River, Maryland. 



The species is one of the most abundant and finest of the Chesapeake 

 Miocene. 



Scapharca (Scapharca) carolinensis Wagner. 



PLATE 33, FIGURE n. 

 Area <,iro/iii<-nsis Wagner, Trans. Wagner Inst., v., p. 9, pi. I, fig. 4; Bronn, Index Pal. 



Nom., p. 93, 1848 ; Syst., p. 283, 1849. 



