CONCHOLOGY. 83 



longed posteriorly, and edged with two rows of very close tuber- 

 cular papillae ; a moderately large abdominal foot, proboscidiform, 

 canaliculated, without byssus ; a very large transversal mouth 

 with well-developed triangular labial appendages ; branchiae nar- 

 row, very long, and united in nearly all their extent. 



Shell. Subnacred, irregular, flat, elongated, subequivalve, ine- 

 quilateral, with summits anterior, distant and flexed inferiorly ; 

 hinge oral and toothless ; ligament undivided, thick, inserted in a 

 round pit excavated in a projecting apophysis upon each valve ; 

 a moderately large subcentral muscular impression, and two very 

 small ones altogether anterior. Inhabits the Indian and Austra- 

 lasian seas. Six living species. One fossil. 



Vulsella hians. Vulsella lingulata. 



V. rugosa. V. mytilina. 



V, spongiarum. V. sevata. 



4. Genus Placuna. PI. IX. 

 Animal. Entirely unknown. 



Shell. Free, subirregular, very fine, almost entirely translucid, 

 flat, subequivalve, subequilateral, slightly auriculated ; hinge alto- 

 gether internal, formed upon the superior valve, which is the 

 smaller, by two elongated, unequal, oblique, crests ; converging to 

 the summit, at the internal side of which a ligament is attached 

 in the form of a V, a single, small, subcentral muscular impres- 

 sion. Inhabits the Indian seas. Two fossils in France. Three 

 living species. 



Placuna sella. Placuna papyracea. 



P. placenta. 



5. Genus Anomia. PI. IX. 



Animal. Much compressed ; edges of the mantle very fine; 

 not adhering, and furnished exteriorly with a row of tentacular 

 filaments ; contractile muscle thick, divided into three parts, the 

 largest of which passes partially across a slope of the inferior 

 valve, and often contains a calcareous substance or small bone, 

 adhering to marine bodies. 



Shell. Adhering, irregular, inequivalve, inequilateral, ostrace- 



