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1283 



TERTIARY FAUNA OF FLORIDA J 



This Cretaceous form appears to be one of the precursors of the Venerida, 

 though its hinge is not as well known as could be desired. It appears to re- 

 semble dementia, but has a smooth surface more or less granulose or punc- 

 tate, with three cardinal teeth in each valve and no trace of lateral teeth. There 

 is no indication of lunule or escutcheon, the internal margins are smooth, and 

 the pallial sinus is exceptionally acute, rising nearly to the hinge-line, and very 

 wide at the base. The form described by Meek from the Cretaceous of Ne- 

 braska is probably an allied but distinct genus in which the shell is smaller, 

 heavier, and smoother, the hinge heavier, and the sinus shorter and more 

 irregular at its anterior basal part. 



It will be noted that the Cretaceous forms referred to this family mostly 

 agree in having no lunular space set off from the rest of the shell, no lateral 

 teeth, and no tendency to radial sculpture or crenulation of the valve margins. 

 We may therefore conclude that these features are characteristic in this family 

 of a more advanced stage of development, though not absolutely restricted to 

 the most modern types. 



Genus MYSIA Leach. 



Mysia (Leach MS.) Lam., An.'s. Vert., v., p. 543, 1818 (in synonymy, as communicated 

 by Leach) ; type Venus undata Pennant ; Brown, 111. Conch. Gt. Brit., ist ed., pi. xvii., 

 figs. 1-2, 1827; 2d ed., p: 98, 1844; Gray, Ann. Mag. N. H., xx., p. 272, 1847; List 

 of Brit. An., Moll., Brit. Mus., p. 5, 1851 ; Philippi, Handb. Conch., p. 343, I&53- 



Lucinopsis Forbes and Hanley, Brit. Moll., i., p. 435, 1848. Type Venus undata Pen- 

 nant. 



Not Mysia Gray, P. Z. S., 1847, p. 195; Conrad, Fos. Medial Tert, p. 30, 1838; Coss- 

 mann, Cat. 111. Fos. Paris, ii., p. 21, 1887, et al; = Diplodonta Brown; nor Mysea 

 Billborg, 1820 (Insecta) ; not Mysia Dall and Simpson, Porto Rico Report, 1901. 



The name Mysia rests on the citation of a synonym by Lamarck under the 

 Lucina undata (Pennant, as Venus) of the latter author. It is connected only 

 with this species, and if retained at all, must be retained for this reason and 

 no other. The fact that Brown, Gray, and others associated other species with 

 the originally unique type does not authorize the adoption of any of these as 

 typical under the rules of nomenclature. The correct course in this instance 

 was pointed out by Gray and Philippi nearly half a century ago. 



The dentition of Mysia consists, in the right valve, of two slender divari- 

 cating cardinals, the posterior grooved or bifid on the edge ; in the left valve 

 are three cardinals, the middle one stout and bifid, the others slender and entire. 

 In Jeffreys' account of the hinge the valves are reversed by some inadvertence. 



