GENUSTHRACIA. 7 



4. THRACIA PHASEOLINA, NOBIS. The French-bean Thracia. 



(Collect. MASS. LAM.) MONTAGU, pi. 1, fig. 2. 



Pi. II, fig. 4. 



Th. testA ovato-oblong, transversal, aequilatera, inaequivalvi, alba, dia- 

 phand, Isevi ; latere posteriore brevi, angulato, truncate. 



Shell ovate, oblong, transverse, equilateral, inequivalve, 

 beaks small ; that of the left, slightly notched. The valves 

 are white, diaphanous and smooth, indistinctly marked with 

 striae of increase, rounded at the anterior side, strongly trun- 

 cated at the posterior side ; the side is bounded outwardly by 

 an obtuse angle, pretty prominent, extending obliquely from 

 the beak to the lower part of the shell. The cardinal edge is 

 thin, and without teeth ; it presents upon the posterior side 

 the beaks with a small, internal, short, triangular hollow, in 

 which is attached a small internal ligament which is apparent 

 externally. The valves are white and shining, internally. 

 The anterior muscular impression is elongated, the posterior is 

 rounded, and is united to the anterior by a palleal impression, 

 deeply notched. 



Length 1 inch 4 lines. Width 11 lines. 



Inhabits the road of Cherbourg, in the Channel, the coasts 

 of England, at Falmouth; the Mediterranean. This same 

 species has been found in the bay of Sea-dogs, but much 

 larger. 



This species was known by Petiver, and has been described 

 by Lamarck under the name of AMPHIDESMA pJiaseolina ; it ap- 

 proaches in its form the THRACIA pubescens, but its lightness 

 and its size materially distinguish it; it differs also from the 

 plicata, for that has very strongly prominent folds, while in the 

 A. phaseolina, the striae of increase are scarcely apparent. 



