228 Bulletin 31 328 



PLATE 27 



Figure Page 



1-6. VencHcardia planicosta Lamarck 77 



Fig. I, var. '"densata'' Con., 35 mm., I^isbon. 



2, var. ^'densata'^ Con., 60 mm., base of Claiborne Bluff. 

 Close to the European /•/flw/Vc'j/'a, especially those ob- 

 tained from the Bracklesham beds of southern England. 



3, the same, 40 mm , 



4, Var. '''jnooreana'" Con., 40 mm., Smithville, Tex. 



5, 68 mm, Claiborne sand variety. 



6, 70 " " " " This is the large, little 

 specialized form abundant in the Claiborne sand and 

 in the Jackson beds of the Mississippi Embayment. It 

 differs but little from some of the earliest Midway 

 specimens, except that it grows larger and shows an 

 obsolescence of costation peripherally. But this 

 latter feature is not shown on young specimens (see 

 pi. 28, fig. I.) 



