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1083 



TERTIARY FAUNA OF FLORIDA 



Oligocene shales near Gatun, on the line of the Panama Canal, Rowell ; 

 Oligocene of St. Domingo, Gabb. 



Shell ovate, solid, heavy, inflated, with high, conspicuous prosogyrate 

 beaks, and a very short and heavy hinge; sculpture of twenty-seven similar, 

 subequal, strong ribs, subtriangular in section, the longer side of the rib in 

 each case inclining towards the middle line of the shell ; interspaces very 

 narrow, not regularly channelled, but rather formed by the sides of the ribs ; 

 the whole shell is covered with fine concentric lineation, and the summit of 

 each rib when perfect carries a line of small nodules, usually rounded or 

 oblong and transverse, and on a few of the ribs near the posterior end more 

 or less A -shaped ; shell nearly equilateral, internal margin fluted, upper part 

 of the posterior margin serrate. Alt. 28, Ion. 20.5, diam. 23 mm. 



This shell has obviously little resemblance to C. subelongatum, and Gabb's 

 statement that it resembles perfectly the recent specimens of that species from 

 the same region is one of those puzzles which are inexplicable. 



(Group of C. isocardia Linne.) 



Cardium (Trachycardium) cestum n. sp. 

 PLATE 48, FIGURE 14. 



Oligocene marl of the Chipola River, Calhoun County, Florida ; Burns. 



Shell moderately large, solid, inflated, slightly oblique, subequilateral ; beaks 

 high and rounded ; sculpture of thirty-four triangular radial ribs, on the 

 summit of which is developed a thin elevated keel of which the summit is 

 somewhat like the top of a T-rail, overhanging at the sides, when intact, and 

 flattened and smooth on top; the sides of the keels and ribs, up to the 

 twenty-second, are vertically striated and sparsely sprinkled with minute 

 granules ; the posterior twelve ribs are asymmetrical, the keels being placed 

 behind the summits of their sustaining ribs and crenulate or surmounted by 

 obliquely set transverse nodules ; the first nine ribs are somewhat similarly 

 imbricate or nodulous, and ventrally in adults near the margin are often 

 pressed over backward and strongly transversely wrinkled with their inter- 

 spaces flat and rather wide, while over the disk the interspaces are chiefly 

 narrow and V-shaped ; different individuals show minor modifications of these 

 details of ornament; interior with the margins fluted, the posterior margin 

 deeply serrate, the internal face with shallow grooves extending upward from 

 the flutings ; hinge normal. Alt. 50, Ion. 40, diam. 36 mm. 



