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963 



TERTIARY FAUNA OF FLORIDA 



Section Chion Scopoli, 1777. Type D. denticulata L. 

 Shell more solid and triangular, sharply truncated, the truncation sculp- 

 tured; the ventral margins sharply fluted. Teeth as in Doiiax s. s., but the 

 laterals distinct ; the shell radially sculptured with the grooves punctate. 



Section Hecuha Schumacher, 1817. Type D. scortum L. 

 Shell large, conspicuously carinate behind, with marked longitudinal sculp- 

 ture in front of the carina. Teeth as in Doiiax s. s., with a sharp groove on 

 the right dorsal margin in front of the socket for the anterior lateral. 



Section Machcerodona.v Romer, 1870. Type D. scalpellum Gray. 

 Shell brilliantly polished, thin, smooth, elongated ; with a sharp carina be- 

 hind but no marked truncation ; ventral margins serrate. Teeth as in Doiiax 

 s. s., but a feeble posterior right cardinal present in addition to the usual two; 

 the anterior right dorsal margin grooved for the edge of the opposite valve. 



Section Platydonax Dall. Type D. Finchii Shy. 



Shell like Machccrodonax but compressed, with the carina obsolete; mar- 

 ginal serration feeble; cardinals as in Donax s. s. but laterals absent. 



Section Grammatodonax Dall. Type Donax madagascariensis Lam. 



Shell short, triangular, compressed ; the surface of the valves deeply ob- 

 liquely furrowed ; the margins finely serrate ; the right valve with a single 

 bifid cardinal ; the left with two simple cardinals, an anterior and a posterior 

 lateral. 



Section Latona Schumacher, 1817. Type D. cuneata L. 



Shell compressed, rounded triangular, solid, the valves subequilateral, con- 

 centric sculpture more conspicuous and frequently rugose behind; there is 

 no distinct truncation or posterior carination; right valve with a deep socket, 

 its ventral edge conspicuous, for the posterior lateral of the opposite valve; a 

 stout bifid and an obsolete anterior cardinal, and a feeble anterior lateral ; left 

 valve with a posterior lateral and two small simple cardinals ; the ventral 

 margins feebly radially striated. This section is intermediate between the 

 true Donaces and Heterodonax in the characters of its shell. 

 Genus Hemidonax Morch, 1870. Type Cardium donaciforme Spengler 

 (-f- Donax picfiis Tryon). 



Shell resembling Chion, but the laterals elongated and the pallial line un- 

 sinuated. 



Donacicardium Vest, 1875, i^ synonymous. 



