FREE INSTITUTE OF SCIENCE 



1293 



TERTIARY FAUNA OF FLORIDA 



This species, doubtless the descendant of the lower Miocene cortinaria, 

 differs from it by having the lamella less crowded and passing, erect and 

 fluted, clear across the disk, without the depression and thickening observable 

 in the other species. A specimen from near the typical locality measures : 

 length 40, height 36, diameter 24 mm. 



The recent species of the coast, representing C. cribraria in the present 

 fauna, is C. intapurpurea Conrad. It has often been confused with the present 

 species, but I regard them as undoubtedly distinct. C. intapurpurea has re- 

 verted in its sculpture to a type more nearly recalling the older Miocene one 

 than that of the upper Miocene: an interesting lesson to some of our enthu- 

 siastic but inexperienced students who propose to overthrow the geological 

 sequence of the strata because the development of some fossils from stage 

 to stage does not fit in with their theoretical scheme of evolutionary progres- 

 sion. 



Section Lirophora Conrad. 

 In this section we have an interesting exhibit of development from forms 

 like those just described to those in which the middle concentric ribbing be- 

 comes dense and heavy, then irregular, more or less coalescent and finally 

 entirely so, and of reversion to the earlier type under circumstances, we may 

 assume, which make it better suited to the environment than that which had 

 been laboriously evolved. In the existing faunas we have C. KeUettii of the 

 Pacific coast, in which the coalescent ribs form a smooth, even surface on the 

 middle of the disk, with high, leaflike expansions distally; forms like C. 

 paphia, in which the ribs have become even and regular ; and still others, 

 wanting the distal expansions, in which the size and sequence of the thick 

 ribs seems to depend on mere luck or accident. So that we may have an 

 evolution from a clear-cut, elegant, attractive type of sculpture to a dull, un- 

 formed, irregular type, which in its turn may meet the difficulties of the 

 situation better than the former. 



Chione (Lirophora) victoria n. sp. 



Plate 55, Figure 17. 



Lower Oligocene of Vicksburg, Mississippi ; P. Crutcher and F. Burns. 



Shell ovate, moderately convex, with low, prosogyrate beaks and a small, 

 cordate, striated lunule ; the escutcheon is flattened and finely striated ; surface 

 sculpture of twenty or more elevated recurved lamellae, more or less depressed 

 and thickened anteriorly, more erect, distant, and higher behind ; the only 



