FREE INSTITUTE OF SCIENCE 



TERTIARY FAUNA OF FLORIDA 



Ixartia Leach, Moll. Gt. Brit., p. 272, 1852. Thracia distorta Montagu (sp.) ; Fischer, 



Man. de Conchyl., p. 1171, 1887; Bucquoy, Dautzenberg et Dollfus, Moll. Mar. de 



Roussillon, ii., p. 740, 1898. 

 Corymya Agassiz, in Sowerby, Min. Conch., ed. Germ., pp. 439, 651, 1843. Type Mya 



depressa Sby. 



Corimya Agassiz, op. cit., p. 577, 1843. 

 Cyathodonta Conrad, Proc. Acad. Nat. Sci. Phila., iv., p. 155, 1849; Fischer, Man. de 



Conchyl., p r 1171, 1887. Type C. undulata Conrad. Lower Cal. 

 Rupicilla Schaufuss, in Psetel's Cat., p. 18, 1867; new name for Rupicola Fleuriau non 



Brisson. 



Momceodesma Fischer, Man. de Conchyl., p. 1171, 1887. Type Thracia Conradi Couthouy. 

 Pelopia H. Adams, P. Z. S., 1868, p. 16 ; P. brevifrons Ads., pi. iv., fig. 16. 

 Ligula (sp.) Montagu, 1808; Brown, 1827. 



This group for an assemblage of such simple characters has had a very 

 complex synonymy. The differences between the various members of it are 

 so slight as to have apparently no more than sectional value. They are as 

 follows : 



Section Thracia s. s. Type T. corbuloidea Blainville. 



Shell concentrically striated, with more or less, fine superficial granulation 

 and a very delicate periostracum ; subrostrate, slightly gapjng behind ; slightly 

 inequivalve, the right valve larger ; the beaks in contact and usually perforated 

 by friction on each other, the hinge-plate fissured below them and edentulous ; 

 the ligament external, the resilium more or less sunken and with, in most cases, 

 a short, transverse .lithodesma in front of it, occupying the fissure in the hinge- 

 plate ; pallial line with a moderate sinus, margins of the valves entire ; the 

 nymphs in the typical forms do not project greatly from the hinge-margin 

 ventrally and are more or less elongated ; the shell is destitute of nacre. 



In this group the lithodesma or ossicle is quite small and frequently lost. 

 The valves cannot be opened after death without snapping it, and it is usually 

 deficient in cabinet specimens. For T. Conradi Fischer made a section, as it 

 was supposed to be without a lithodesma, but I have found it present in the 

 young, though so small that it has been generally unrecognized. The siphons 

 are entirely separated and have a very few terminal papillae. 



Section Ixartia Leach. Type T. distorta Montagu. 



Valves irregular from the nestling habit ; the resiliifer short, prominent, 

 projecting into the cavity of the shell, a lithodesma present. 



Pelopia H. Adams, Rupicola Fleuriau, not Brisson, and Rupicilla Schau- 

 fuss are supposed to be synonymous. 



