TRANSACTIONS OF WAGNER 

 1450 



TERTIARY FAUNA OF FLORIDA 



Section Cyrenodonax Dall, 1903. Type C. formosana Dall.'^ Recent 

 in Formosa, at the mouth of the Tamsui River ; Hungerford. 



Shell small, thin, delicate, donaciform, with three very oblique, slender 

 cardinals in each valve, the middle one feebly bifid, the others nearly parallel 

 with the hinge-line; the anterior end of the shell much longer than the pos- 

 terior ; the laterals elongate, slender, sharply crenate ; the pallial line entire, 

 the margins smooth. 



This recalls Donacopsis, but is inflated, entirely without any sulcata radia- 

 tion or crenulation of the valve-margin, has better developed teeth, and an 

 entire pallial line. 



Subgenus Cyanocyclas Ferussac, 1818. Type Corhicula limosa Maton. 

 American waters. 



Shell resembling Corbie iila but with a small, angular pallial sinus, the animal 

 viviparous and confined to the streams of Central and South America and 

 Mexico. 



Ferussac's genus included species of Egeria and Corhicula (both older 

 names) and the single species of Maton, which must retain the name. Neo- 

 corbicula Fischer, 1887, is synonymous, and Agassiz, apparently not under- 

 standing the reference to the violet color in all these shells, altered the name to 

 Cyrenocyclas. 



It is somewhat remarkable that the only species of Corhicula known to our 

 eastern Tertiaries should belong to the typical section, while all those of the 

 western lake beds, from the Cretaceous to the Pliocene, as far as their char- 

 acters have been recorded, belong to Cyanocyclas. 



Corbicula densata Conrad. 

 Cyrena densata Conrad, Proc. Acad. Nat. Sci. Phila., i., p. 324, 1843; Fos. Medial Tert., 



p. 68, pi. xxxix., fig. 2, 184s; Emmons, Geol. Rep. N. Car., p. 290, fig. 2150, 1858; 



Tuomey and Holmes, Pleioc. Fos. S. Car., p. 77. pl. xx., fig. i, 1858; Conrad, Proc. 



Acad. Nat. Sci. Phila., xiv., p. 576, 1863 ; Meek, S. I. Checkl. N. Am. Miocene Foss., 



p. 9, 1864; Prime, Mon. Corbicula dee, p. 31, 1865. 



" Near Petersburg, Va.," Tuomey ; Pliocene of North Carolina, Emmons ; 

 of South Carolina, on the Waccamaw River, at Nixon's marl-pit, C. W. John- 



's' Shell plump, polished, with low but turgid beaks, covered with an olivaceous peri- 

 ostracum, sometimes with violet rays or with darker zones; the interior violet. The 

 beaks at the posterior third. Length 12, height 8, diameter 6 mm. 



