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TERTIARY FAUNA OF FLORIDA 



speculation. The shell is said by Defrance to be about five millimetres in 

 length. 



Section Chainclca Morch. Type Venus gallina Linne. 



Sculpture of narrow, close concentric waves or low lamellae without radials 

 or distal lamellation : teeth entire ; escutcheon and lunule smooth ; the ligament 

 exposed. The siphons are partly united. 



Subgenus Gomphina Morch. Type Venus undulosa Lamarck. 



Valves more or less extended behind and pointed ; surface usually smooth 

 and polished ; inner margins not crenulate, anterior left and posterior right 

 dorsal margins beyond the hinge-plate grooved to receive the bevelled edge of 

 the opposite valve ; lunule long and narrow ; the posterior right and two 

 anterior left cardinals grooved ; the ligament exposed ; pallial sinus short, 

 free, and rounded in front. 



Section Gomphina Morch s. s. Type Venus undulosa Lam. 



Lower edge of the right nymph and upper edge of the left posterior car- 

 dinal with reciprocal rugosities. Most of the species of this group are heavy, 

 inequilateral, solid, and very tumid. Tapes pinguis Sowerby, in the Thesaurus, 

 pi. cxlvi., figs. 20-23, is really more typical of this group than the nominal 

 type. Marcia Chenu, not Fischer, is synonymous. 



Section Macridisciis Dall. Type Venus ceqnUatera Sowerby. 



Nymphs and teeth smooth, entire ; valves in general more compressed, 

 equilateral, and trigonal than in the preceding section ; less heavy, and some- 

 times with feeble striation distally. 



Venus faba Reeve and F. fuinigata Sowerby seem to belong to this sec- 

 tion. It is Gomphina H. and A. Adams, not Morch. 



The American species of the section Chione are naturally divisible into 

 three groups, each of which has a representative in each horizon from the 

 Oligocene up. These are (i) the group of C. cancellata, which has the shell 

 trigonal and the concentric lamellae rather distant; (2) the group of C. sub- 

 rostrata Lamarck, which has the sculpture delicate and the concentric lamellae 

 rather close and low, with the shell produced and compressed behind ; and 

 (3) the group of C. pubera Valenciennes, which has the concentric lamellae 

 close, very numerous, and crenulate, so that the interspaces have a punctate 

 appearance. 



