108 12 
Long. 5—85 mm. 
Distribution: — Singapore, Mergui Archip., Andamans, Tranquebar, Ceylon, 
Panjim and Goa, Bombay, Karachi, Persian Gulf, Aden. — Annam, Poulo-Condor, 
Philippines, China, Japan, North, East and West Australia. 
Pl. auriculata, Yoldi' from the Red Sea is only a form of Pl. placenta L. which 
anteriorly and posteriorly is flattened in an ear-like manner above the dorsal 
margin. Such forms also occur among the specimens from the Gulf of Siam. 
A. WILLEY® (loc. cit. p. 87, Fig. 1) mentions and figures specimens of Pl. placenta 
from Ceylon with such ear-like lobes occurring on either side of the hinge-line, 
especially in young individuals. 
Placuna papyracea, Lam. 
Ephippium parvum papyraceum Anglicanum seu Polonicum, Cuemnirz, Conchyl. Cabin., VI, 1785, p. 
114, pl. 79, fig. 715 
Placuna papyracea, LAMARCcK, Hist. nat. d. anim. s. vert., ve ae J, 1819, p. 224. — ed. 2, 1836, VII, p. 270. 
= Encyclop. méthod., pl. 174, 
= = - MARTINI u. CHEMNITZ, Bees on VII, 1. Abth., p. 65, pl. 5, fig. 2. 
Placenta peeraraaie Rerzius, Diss. sist. nova testaceor. genera, 1788, p. 16. 
Koh Lan, 30 fathoms, mud (1). Between Koh Rin and Cliff Rock, 15 fathoms (7). 
N. of Koh Kam, 5 fathoms, gravel (12). East of Cape Liant, 9 fathoms, shells (1). 
Koh Chuen, 30 fathoms (2). Koh Kahdat, 1—5 fathoms, sand with stones (1). 
Long. 19—84 mm. 
Distribution: — Mergui Archip. — Philippines, Amboina (?), Aru Isl., Sorong, 
Australia. 
Reeve, and J. E.Gray® attribute much importance to the reciprocal length of 
the two hinge-leeth, to their position with reference to each other, and to the angle 
formed by them; in the case of young individuals these can by no means be used 
as specific characters (in older specimens they may be employed as such); in 
specimens, for example, of P. papyracea, Lam. and P. placenta L. (of about 20 mm. 
in breadth) from the Gulf of Siam, there is no difference whatever with regard to 
these points: on the other hand, the sculpture and consistency of the shell, which 
in most cases is characteristic in each species of Placuna, is a far better specific 
character, being also constant. 
Placuna (Placunema) sella, Gmel. 
Ephippium anglicanum maximum, Curemnirz, Conchyl. Cabin., VIII, 1785, p. 111, pl. 79, fig. 714. 
Anomia Sella, GMELIN, Systema Naturae, ed. XII, 1790, p. 3345, No. 27. 
Placuna sella, — LAMARCK, Hist. nat. d. anim. s. vert., VI, p. 1, p. 224. — éd. 2, VII, p. 270. 
' Moncu, Catalog. conchyl. qu reliq. com. de Yoldi, II, p. 68. The original specimen is in my 
collection. 
° Spolia Zeylanica, vol. V, part XVII, Colombo, 1907, pp. 33—57 
5 Proc. of the Zool. Soc. London, XVI, 1848, p. 114. 
