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I22S 

 TERTIARY FAUNA OF FLORIDA 



nymphs and strong ligament, a carious process goes on below the beaks, re- 

 sulting in the decay of the shelly matter and the formation of a small cavity 

 under the anterior end of the ligament which sometimes encroaches on the 

 posterior cardinals* This has been mistaken by some writers for a normal 

 formation, but is merely the result of decay due to the access of seawater and 

 senility of the adjacent portion of the ligament. 



A. Anterior and posterior laterals present, the lunule impressed but not 



definitely limited. 



Genus DOSINIOPSIS Conrad. , 



Dosiniopsis Conrad, Proc. Acad. Nat. Sci. Phila. for 1864, p. 213 (D. Meekii Conrad, 

 loc. cit.) ; Meek, Pal. Upper Missouri, p. 179, 1876; Tryon, Str. and Syst. Conch., p. 

 178, 1884; Fischer, Man. de Conchyl., p. 1079, 1887. 



Cytherea Stoliczka, Cret. Pel. India, p. 151, 1879. 



The type of this remarkable group is Cytherea lenticularis Rogers, Trans. 

 Am. Phil. Soc., vi., p. 372, pi. xxviii., fig. i, 1839, a more solid and heavy 

 variety of which was named by Conrad D. Meekii* BuO- rW 



It is an orbicular shell, with a dark and heavy periostracum, which is fre- 

 quently well preserved in the fossils, covering a concentrically striated surface. 

 The inner margffts are smooth, the pallial sinus is short, free, acutely angular, 

 and ascending. ,The lunule is impressed but not distinctly circumscribed, and 

 there is no defined escutcheon, though the area in which the ligament is seated 

 is depressed below the hardly carinated dorsal margins. The hinge is strong 

 and remarkable in being the only genus of the family in which there is a dis- 

 tinctly developed posterior lateral tooth. This enters an excavated socket in 

 the left valve which is not bounded by any laminae. The nymphs are corru- 

 gated and there is a strong corrugated left anterior lateral. The posterior right 

 cardinal is broad and deeply channelled above. If Stoliczka had seen the typical 

 species he would not have referred the group to Cytherea Lamarck. The dental 

 formula is L - Q-XIOIOIQ.OIO > The genus, so far, is only known positively from 



R. i.xoioioi.ioi 



the Eocene of France and eastern North America; the two British species, 

 Venus plana and Cyprina planata of Sowerby, referred to Dosiniopsis by Mr. 

 Conrad in 1866, appear from the figures to be respectively a Meretrix and a 



* See Clark, U. S. Geol: Survey, Bull. 141, p. 78, pi. xviii., figs. ia-ig, 1896. 



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