TRANSACTIONS OF WAGNER 



TERTIARY FAUNA OF FLORIDA 



five, three twenty-six, and three twenty-seven ribs. The normal number of 

 ribs for this species would therefore seem to be twenty-one to twenty-five. 



In the basal Miocene, as at Darlington, South Carolina, the adults of 

 this species show radial threads towards the margin, which, reticulating with 

 the concentric sculpture, give the shell a little the look of Lyropecten, like 

 cdgecoinbensis, and, in fact, the shells are intermediate between the Lyropectens 

 and Plagioctcnium. The latter section has its characters well in equilibrium 

 hardly before the recent fauna, though in this series they can be seen in the 

 making. 



The different mutations, though intergrading considerably, may, for con- 

 venience, be distributed as follows : 



Pecten eboreus var. darlingtonensis Dall. 

 Miocene of Darlington, South Carolina. 



Shell large, radially striate on the disk near the margin ; the ribs angular, 

 well marked, twenty-one to twenty-four ; the concentric sculpture fine. 



Pecten eboreus var. eboreus Conrad. 

 Miocene of Suffolk, Nansemond River, Virginia. 



Shell large, with no radial strise on the disk ; ribs low, rounded, with 

 shallow interspaces, twenty-three to twenty-seven ; concentric sculpture distant, 

 feeble. 



Pecten eboreus \'ar. yorkensis Conrad. 

 Miocene of York River, Virginia. 



Like variety eboreus, but with the ribs more rectangular in section, twenty- 

 one to twenty-five. 



Pecten eboreus var. comparilis Tuomey and Holmes. 



Miocene of South Carolina. 



Shell stunted, rather convex; the backs of the strong rectangular ribs 

 bare, the interspaces and sides of the ribs with strong, crowded, concentric 

 lamellae ; twenty-three ribs, the interspaces deeply notched at the margin. 



This form bears to the typical eboreus much such a relation as, in P. 

 gibbus, variety dislocatus does to variety irradians. 



Pecten eboreus var. solarioides Heilprin. 

 Pliocene marls of Florida. 



Shell large, like variety eboreus, but the ribs squarish and distant, nineteen 

 or twenty. 



