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11 59 



TERTIARY FAUNA OF FLORIDA 



We therefore arrive at the conclusion that the name Rochefortia must be 

 adopted for the genus, which may be characterized as follows : 



Shell small, ovate or rounded-quadrate, anterior end longer ; hinge with 

 a short internal subunibonal resilium and traces of an amphidetic, obsolete, 

 external ligament ; on either side of the resilium the cardinal margin bears a 

 simple oblique lamina, the pair divaricating from the umbo and without any 

 hook at the proximal ends ; they are separated usually in one valve from the 

 dorsal margin by a groove parallel to it, and above this groove the margin in 

 some cases is thickened so as to form another lamina; the single laminae of 

 the opposite valve, sometimes represented only by inflected and bevelled ex- 

 tensions of the valve margin, are received into the grooves above the laminae 

 of the first-mentioned valve, are often longer than the latter and themselves 

 of unequal length ; the double short laminae, when both are present, are usually 

 in the left valve, and the right anterior lamina is longer than the right posterior 

 one. From Bernard's researches into the development of the hinge it is evident 

 that these laminae represent the secondary laminae of such forms as the Vene- 

 r'uUc before the latter break up into cardinal and lateral teeth properly so 

 called; but in rare instances the laminae of the present group begin to show 

 signs of a tendency to separate, so that the distal portions are more elevated 

 than the medial part and the former might be taken for laterals and the proximal 

 ends for obscure cardinals, which in a genetic sense they really are. The 

 ventral portion of the resilium carries a calcareous coating which in well- 

 developed specimens is distinguishable as a lithodesma or " ossicle." Type 

 R. australis Velain. 



Subgenus Rochefortia s. s. 



Shell ovate or rounded-trigonal, periostracum adherent, usually polished ; 

 individuals free or domiciliary in the burrows of crustaceans. 



PSubgenus Pythinella Ball. 



Shell transverse, with a basal insinuation; periostracum rude, individuals 

 commensal with and (?) attached by a byssus to the bodies of Crustacea; 

 hinge as in Rochefortia. Type Montacuta cuneata Verrill and Bush ; North 

 Carolina. 



This subdivision corresponds, in the line of Rochefortia, to Pseudopythina 

 in the line of Erycina, Pythimt in the line of Bornia, and Hindsiclla in the 

 line of Sportella. 



