PLACENXADa;. 
3 
2. PLACtTNA PAP'S RACEA. 
Shell rather four-sided, nearly flat, thin, hyaline, white and pur- 
ple varied. 
Placuna papyracea, Larnk. Hist. vii. n. 2. 
Ephippium parvutn, Chemn. Conch, viii. 1. 79, f. 719, cop. E. M. 
t. 174, f. 2. 
Anomia Sella junior, DiUic. R. S. i. 297. 
Placenta papyracea, Gray, Proc. Zool. Soc. 1848. 
a, b, c, d. Shell thin, slightly flexuous, more or less purple 
varied. China. 
e. Single valve; flat, thin, brown, transparent edges. India. 
Presented by Dr. Horsfield. 
f. Flat; front, and especially the hinder edge notched, thin. 
Pale purple spotted. Australia. Presented by the Earl of 
Derby. 
Perhaps only the young of P. Sella. 
3. Placuna Lixcolnii. 
Shell flat, rather solid, subopaque, outline suborbicular, rounder 
before and behind ; ridges of the hinge elongate, longer than they 
are separate from each other at the base. 
Placenta Lincolnii, Gray, P. Z. S. 1848, 113; Moll. t. 3. 
a. Australia; Mr. W. Davison. Presented by Abraham Lin- 
coln, Esq. 
This species is named after the late Mr. Abraham Lincoln, who 
kindly presented the specimen here described, and who was well 
known for his fondness I'or conchology and the liberality with which 
he allowed persons to use his extensive collection. 
2 PLACENTA. 
Shell semitransparent, flat, outline suborbicular ; ridges of the 
hinge very gradually diverging from each other, the hinder ridge 
much the longest. Muscular scar rather in front of the middle 
of the hinge. 
Placenta, Retzius, Dissert. 15, 1788 (not Klein) ; Sclium. N. S. 
113, 1817; Gray, P. Z. S. 1848. 
Placuna sp. Solander, 1785, fide Chemn. Cab. viii. 116 ; Bruy. E. 
M. t. 174, 175, 1792 ; Lamk. Hist. 2 ed. vii, 270. 
