TRANSACTIONS OF WAGNER 

 QIO 



TERTIARY FAUNA OF FLORIDA 



while the last reviser, Fischer, would restrict Mesodesma s. s. to the Donacilla 

 type, use Machcena for M. novceselandice, Eryx Swainson for M. glabratum, 

 in other respects following Gray. 



Lastly, to close the record of the nomenclature of this group, Ervilia 

 Turton (1822) and C&cella Gray, 1853, may be mentioned, and Conrad's Tri- 

 quctra, 1846, for which he substituted MactropSK in 1854, a genus based on 

 two Claibornian species in which the first stages of submergence of the liga- 

 ment are well exemplified. 



A number of the names above cited arc not available for reasons which 

 may be stated. Paphia is preoccupied by Bolten, who has precedence of one 

 year. Donacilla was not characterized, but if we adopt M. donaduin Lam. 

 (chilensis Orb.), Deshayes's first species, as the type of Mesodesma, Donacilla 

 can be revived in a sectional sense for the smooth-toothed cuneate species, 

 as was done by- Gray; in which case Ccronia Gray becomes an exact syn- 

 onyme of Mesodesma. Paphies Lesson has precedence of Mach&na for M. 

 novtzzelandice (= M. australis Gmelin). The original Anapa Gray is a 

 synonyme of Lascea (Leach) Brown, and cannot be used for the Tasmanian 

 genus to which Gray later applied it. The family will then stand as follows : 



Subfamily MESODESMATIN./E. 



Shells heavy, with a pallial sinus more or less developed ; siphons sepa- 

 rate from their bases ; shell substance porcellanous, epidermis conspicuous ; 

 ligament inconspicuous, generally inserted on the upper part of the posterior 

 border of the " cartilage-pit," if wholly external more or less obsolete ; resilium 

 narrow, oblique ; hinge with an anterior and posterior lateral in the left valve, 

 fitting between laminae in the right valve ; recent species with a single narrow, 

 long left cardinal tooth, with a short posterior arm which crosses the apex 

 of the cartilage-pit ; right cardinal lamellar feeble, obsolete ; Eocene species 

 have the cardinals normal. 



Genus MACTROPSIS Conrad. 



Mactropsis Conrad, Proc. Acad. Nat. Sci., vii., p. 30, 1854. 

 Triquetra Conrad, Am. Journ. Sci., 2d Ser., i., p. 217, 1846; not Blainville, 1818. 



This differs from all the recent forms in that the combined ligament and 

 resilium are very near the dorsal border, and the cardinal teeth are distinct, 

 with subequal arms. The laterals are striated transversely. As the sub- 

 mergence of the resilium progressed in later species, it gradually encroached 



