JOUANNETIA. 329 



gape elosed in the adult, with the exception of Talona, in 

 which the front gape is nearly closed. 



Sjiecies of Pholadidea. 



melanura, Sow. sulcata, Brown. 



papyracea, Soland. trideus, Sow. 



quadra, Sow. tubifera, Sow. 

 spathulata, Sow. 



Genus TALONA, Gray. 



Siphons with horny or shelly valves at their base. 



Shell with the front gape small; dorsal valves two, 

 moderate, diverging. 



Ex. T. explanata, Spengler, pi. 90, fig. 2, 2, a. 



In this genus the bases of the siphons are protected by a 

 shelly tube, and the valves are nearly closed anteriorly. 

 There is but one species at present known, the Pholas ex- 

 planata of Spengler or P. clausa of Gray. 



Genus JOUANNETIA, Desmoulins. 



Siphons naked. 



Shell globose, inequivalve, the front gape at length closed 

 by a callous plate; right valve produced posteriorly, the 

 left overlapping the opposite valve ; dorsal plate single ; 

 umbonal process none. 



Syn. Pholadopsis, Conrad. Triomphalia, Sow. 



Ex. J. globosa, Quoy and Gaimard, pi. 90, fig. 3. 

 Shell, J. globosa, fig. 3, a, 3, b. 



This genus, first established by M. Desmoulins on a 

 fossil species, J. semicandata, from Merignac, found 



