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circular lobe at the base of their outer side, and a wide and deep sinus 
in their upper half,” which certainly is not the case with my speci- 
mens, the notch being neither wide nor deep, nor the lobe at the base 
at all distinctly marked. Neither is there any great resemblance to 
Mr. Bell’s figure, taken from Brongniart’s; the ears in that being 
much narrower in proportion to their length, with the sinus near the 
top of the outer side. It agrees however very nearly with the de- 
scription and figure given by the latter naturalist from the specimen 
found by him near Dover, and there can be no doubt of its identity 
with his specimen of Vesperti/io emarginatus. 
2. On THE SPEcIES oF THE GENUS PLacEenTA OF RETZIUS. 
By J. E. Gray, Esa., F.R.S. zere. Erc. 
(Mollusca, pl. 1. fig. 1.) 
Lamarck describes three species of this genus, depending on the 
general outline and the waved or flat form of the shell, characters 
which are liable to considerable variations, as may be found on the 
mere inspection of any considerable number of specimens. 
I have observed that the hinge forms a more permanent character, 
and affords the means of dividing the species into two sections, and 
furnishes characters which separate them from each other. In both 
subgenera the right valve is the flattest, and bears the ridges of the 
hinge. 
Sect. I. Placuna, sp.Lamk.=Ephippium,Chemn.; Placenta 3, Schum. 
Shell purplish, subopake ; hinge-ridges rapidly diverging from one 
another at about the angle of 45 degrees. Muscular scar under 
the centre of the hinge. The ridges of nearly equal length. 
1. Placenta Sella.—Shell flexuous, outline rather rhombic, being 
straight in front and rather notched behind; the ridges of the hinge 
not longer than they are separate from each other at the base. 
Anomia Sella, Gmelin, S. N. 3345, 1788. 
Placuna Sella, Lamk. Hist. N. 2. 
Ephippium anglicanum maximum, Chemn. C. viii. t. 79. f. 714. cop. 
E. M. t. 174. f. 1. 
Placenta Ephippium, Retz. 1788. 
Inhab. China, India. 
®. Shell nearly flat, subquadrangular. 
Inhab. Australia. Brit. Mus. 
2. Placenta papyracea; Placuna papyracea, Lamk. Hist. N. 2= 
Ephippium parvum, Chemn. Conch. viii. t. 79. f. 719. cop. E. M. 
t. 174. f. 2. 
3. Placenta Lincolnii.—Shell flat, outline suborbicular, rounder 
before and behind ; ridges of the hinge elongate, longer than they are 
separate from each other at the base. 
Inhab. Australia; Mr. W. Davison. British Museum. 
I wish to name this species after my excellent friend Mr. Abraham 
Lincoln, who kindly presented me with the specimen here described, 
and who is well known for his fondness for conchology and the libe- 
rality with which he allows persons to use his extensive collection. 
