CONCHOLOGY. &3 
longed posteriorly, and edged with two rows of very close tuber- 
cular papilla ; a moderately large abdominal foot, proboscidiform, 
canaliculated, without byssus; a very large transversal mouth 
with well-developed triangular labial appendages ; branchie nar- 
row, very long, and united in nearly all their extent. 
Shell. Subnacred, irregular, fiat, 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. evata. 
4. Genus Placuna. Pl. IX. 
/Amimal. Entirely unknown. 
Sheli. 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. ‘T'wo fossils in France, Three 
living species. 
Placuna sella. Placuna papyracea. 
P. placenta. 
5. Genus JAnomia. 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- - 
