OF EVOLUTION. 89 



however, a fauna appears to have been 

 developing in place for probably hundreds of 

 thousands of years, so that the unequivocal 

 ancestors of many of the living forms can be 

 found in the fossil remains that preceded them. 

 I have brought before you several such forms, 

 which it was my pleasure to discover two win- 

 ters ago in the interior wilds of the peninsula 

 of Florida. 



One of these you will readily recognize as a 

 wing-shell, of the type of the large pink 

 conch which is found on so many of our 

 mantel tops ; I have named the species, in 

 honor of the distinguished President of this 

 Academy, Strombus Leidyi. Alongside of it I 

 have placed the stromb most nearly related to 

 it in the recent fauna, Strombus accipitrinus, an 

 inhabitant of the Floridian and West Indian 

 coasts. In comparing the two together it will 

 be seen that the principal distinguishing charac- 

 ters lie in the particular form of the wing, and in 

 the tuberculation of the body-whorl or chamber, 



