TRANSACTIONS OF WAGNER 

 580 



TERTIARY FAUNA OF FLORIDA 



C. Lcdella Verrill, 1897 {^ Jiinonia Seguenza, 1876, not of Hiibner). Type 

 L. messanensis Seguenza. 

 Differs from Jiipiicria by having a straighter rostrum, with the margin 

 retuse below it. These differences disappear in a large series of 

 species, and the transition between slightly rostrate forms and those 

 with rounded posterior extremity is complete. Lcda pontonia Dall, is 

 a typical, but unusually \diYge,Jitpiteria. 



cc. Lediiia Dall. Type L. cborca Conr., i860, not 1846, = L. smirua Dall, 

 Eocene. 



Shell solid, strong, arcuate below, both ends evenly rounded, valves 

 nearly equilateral, smooth. 

 This section has been frequently placed with Yoldia. 



D. Perrisonota Conrad, 1869. Type L. protexta Conr., Eocene. 



Shell elongate, smooth, compressed, inequilateral, with valves closed in 

 front, the rostrum very long, not ribbed, and slightly gaping at the end. 



The recent L. Carpcnteri and L. extemiata Dall belong to this group. 



E. Adraiia H. and A. Adams, 1858. Type L. clongata Sby., recent. 



Very elongate and thin, flattish, subequilateral, gaping at both ends. 



This group, as far as the shell is concerned, approaches very near some 

 Yoldias, but on the other hand a complete series of species (such as L. Giippyi 

 Dall, Oligocene, Trinidad) connect it by easy stages with typical Lcda. 



It should be borne in mind that the length and attenuation of the rostrum 

 is not necessarily correlated with the length of the siphons, for many species 

 with an extremely long rostrum have a very small and shallow pallial sinus ; 

 while others which are not rostrate at all (ex. Yoldia scapania Dall) have a 

 large and deep sinus. The correlation is probably with the mantle lobes, 

 which in the Nuculacea generally are apt to be peculiarly modified and often 

 exhibit special appendages. While the typical members of the groups above 

 alluded to seem quite distinct from one another, large series of species may 

 be relied upon to bridge any of the indicated gaps. 



The principal stress in the classification of the Nuculacea has been placed 

 on the position of the ligament and resilium, after the grand division into 

 pearly Nucidida, without siphons, and porcellanous Ledidcs, with siphons, had 

 been made. 



