TRANSACTIONS OF WAGNER 

 lOQO 



^ TERTIARY FAUNA OF FLORIDA 



There is practically no smooth area between the most anterior ribs and the 

 hinge-margin in a typical specimen. The details of the ornament vary more 

 or less but are more constant than one would expect in structures whose 

 minute details can hardly affect the economy of their builder, but are the result 

 of minute modifications of the mantle margin. 



I have been at the trouble to count the ribs of fifty-five specimens of this 

 species from all parts of its range and record the result, the figures represent- 

 ing the number of ribs and those following in parentheses the number of 

 specimens having the number of ribs indicated by the units preceding the 

 parenthesis : 



30 (2), 31 (9), 32 (5), 33 (8), 34 (7), 35 (8), 36 (6), 2,7 (5). 39 (3). 

 40 ( I ) , 41 ( I ) ■ 



The only generalization that seemed authorized is that the ribs are less 

 numerous in specimens from near the northern border of the ralige of the 

 species, and also in the fossils ; the specimens with thirty-seven to forty-one 

 ribs are nearly all from the southern half of the area inhabited. There was no 

 diminution of ribs towards the southern extreme of the range and no regu- 

 larity in the variations of the murication which could be correlated with 

 difference of habitat. 



(Species of the group of C. clongatuiu.) 



Of this group, which resembles species of the C. isocardia type with the 

 ornament removed from the tops of the ribs, and existing, if at all, only on 

 their sides in the interspaces, we have two unidentified species indicated by 

 fragments in the Bowden Oligocene marl of Jamaica: one, C. decUve Gabb 

 (1881, very similar to C. inconspicmun Guppy), from the Pliocene of Costa 

 Rica, and the following species : 



Section Acrosterigma Dall. 

 Cardium (Trachycardium) Dalli Heilprin. 

 Cardium Dalli Heilprin, Trans. Wagner Inst., vol. i., p. 131, pl- i6a, fig. 70. 1887. 



Pliocene marls of the Caloosahatchie and Shell Creek, Florida: Willcox 

 and Dall. 



This magnificent species has thirty-five ribs, of which seven belong to the 

 posterior area and are flattened and grooved, with traces of minute spinules 

 in the interspaces near the hinge; the cfther ribs are broadly arched, almost 

 flat, nearly smooth, with faint longitudinal and concentric stria; : the edges of 



