TRANSACTIONS OF WAGNER 

 12^6 



^ TERTIARY FAUNA OF FLORIDA 



Harris ; an internal cast from the Miocene clays of Gay Head, Martha's Vine- 

 yard, Massachusetts, may possibly be referable to this species. 



This species is quite similar to C. daricna, but more delicate and with fewer 

 and less prominent undulations. 



dementia Gray! Dall. 

 Plate 2,7, Figure 12. 

 dementia Grayi Dall, Trans. Wagner Inst., iii., part v., p. 1 193, pi. xxxvii., fig. 12, 1900. 



Uppermost OHgocene at Oak Grove, Santa Rosa County, Florida ; Burns. 



Shell thin, convex, rude, concentrically coarsely and irregularly striated, 

 near the beaks concentrically vmdulated, without lunule or escutcheon ; internal 

 margins smooth, adductor scars large, pallial line with a long, narrow, acute 

 sinus extending forward more than two-thirds the way from the posterior to 

 the anterior adductor ; cardinal teeth entire, the middle cardinal strongest. 

 Height 55, length 63, diameter 32 mm. 



This fine species is not imlike the C. Vatheletii Mabille, living in Korea. 



The only recent species now known to inhabit American waters is C. solida 

 Dall, from the west coast of Mexico ; the C. sabdiaphana Carpenter, recent 

 and fossil in California, is not a member of this genus, and the C.f gracillima 

 Carpenter is unidentifiable and founded on a nepionic shell which has not 

 assumed adult characters. 



Subfamily MERETRICIN.^. 



We now come to a group a large part of which was formerly included in a 

 general way under Meretrix or Cytherea, but which, on closer study than it 

 has usually received, we are obliged to divide into a number of separate groups 

 or genera. A few general remarks may not be' out of place here. This great 

 group contains a large proportion of the Veneridce and many of the more 

 elegant and beautiful forms. The}' are characterized in general by a smooth 

 or concentrically sculptured surface, often with a vernicose periostracum ; 

 smooth inner margins to the valves ; a single anterior lateral lamella in the 

 left valve, received in a pit or between two less conspicuous lamellae in the 

 opposite valve ; three cardinal teeth in each valve, of which some may be 

 grooved or bifid ; the lunule circumscribed and defined by an incised line, the 

 escutcheon not defined or circumscribed except sometimes by color markings 

 or the absence of SLirface sculpture ; the ligament is external though sometimes 

 depressed, the pallial sinus varying from almost obsolete to deep and angular ; 

 siphons of moderate length with papillose orifices, the tubes united for a great 



