2 
CATALOGUE OF 
b. Hinge-ridge transverse, elevated on a broad and high process. 
3. Hejiiplacuna. A small pit in front of the base of the hinge- 
ridge. Fossil. 
a. Hinge-ridges linear, diverging, only slightly raised. 
1. PLACUNA. 
Shell purplish, subopaque; hinge-ridges rapidly diverging from one 
another at about the angle of 45 degrees, of nearly equal length. 
Muscular scar under the centre of the hinge. 
Placuna, iSo/auder, 1785, fide CAema. Conc’A. viii. 116; Humph. Mus. 
Calonn. 1797 ; Lamk. Syst. 135, 1801. 
Placuna, sp. Brug. E. M. t. 174, 175, 1792 ; Lamk. Hist. 2 ed. vii. 
270. 
Ephippium, Bolten, Mus. 1798, 2 ed. 116, 1819; Chemn. Conch. 
vii. 116. 
Placenta, j8., Schumacher, N. Syst. 113, 1817. 
Placuna pectinoides, Lamk. Ency. Meth. t. 175, f. 1-4, is a species 
of Plicatula, Desh. in Lamk. Hist. 2 ed. vii. 271. 
1. Placuna Sella. 
Shell flexuous, outline rather rhombic, being straight in front and 
rather notched behind, rather thick, purple ; the ridges of the hinge 
not longer than they are separate from each other at the base. 
Anomia Sella, Gmelin, S. N. 3345, 1788 ; Dillw. R. S. i. 297. 
Placuna Sella, Lamk. Hist. vii. 270, No. 1. * 
Ephippium anglicanum maximum, Chemn. C. viii. t. 79, f. 714, 
cop. E. M. t. 174, f. 1. 
Placenta Ephippium, Retz. 1788. 
Placenta Sella, Gray, Proc. Zool. Soc. 1848, 113. 
a, h. Adult. Purple, flexuous. China. 
c. Nearly adult. Flexuous. China. Mus. Cracherode. 
d. Young. Single valve; flat, purplish. India. Presented 
by Dr. Horsfield. 
e. N. W. Australia. Presented by the Earl of Derby. 
Var. /3. Shell nearly flat, subquadrangular, notched before and 
behind. 
