PETRICOLA. 



GENERIC CHARACTER. 



Shell bivalve, transverse, subtrigoiiate, or oblonj^, ine- 

 quilateral, rounded behind, anteriorly narro^Yed and a lit- 

 tle gaping; hinge having one or two teeth on each valve, 

 or upon one of the valves only ; palleal impression pro- 

 foundly sinuous anteriorly. 



Animal with two syphons, divided only at tip, unequal 

 in length and diameter, contractile within the shell ; 

 mantle thicker on the margin and united, with a very 

 small opening for the rudimental conic fool ; mantle very 

 small, transverse, chieily concealed by two lips, which are 

 extended laterally into small triangular palpi. 



OBSERVATIONS. 



Lamarck in his last work, united Rupellaria of Bellevue 

 to his Petricola, in his family Lithophaga, which, as its 

 name implies, contains those genera of shells, wliich arc 

 destitute of accessory pieces and have the remarkable pro- 

 perty of penetrating calcareous rocks and thus establish- 

 ing for themselves a permanent and secure dwelling. This 

 family consists of three genera, Saxicava, Petricola and 

 Venerupis, which are closely allied. The hinge of the 

 former is destitute of teeth, or, in some instances has only 

 obsolete tubercles, and the syphons of the animal are longer 

 than in the present genus and united to the extremity in 



PI. 6V. 



