108 12 



Long, f)— 85 mm. 



Distribution: - Singapore, Mergui Archip., Andamans, Tranqiiebar, Ceylon, 

 Panjim and Goa, Bombay, Karachi, Persian Gulf, Aden. — Annam, Poulo-Condor, 

 Philippines, China, Japan, North, East and West Australia. 



PI. auriculala, Yoldi ^ from the Red Sea is only a form of PI. 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. 37, Fig. 1) mentions and figures specimens of PI. placenta 

 from Ceylon with such ear-like lobes occurring on either side of tlie hinge-line, 

 especially in young individuals. 



Placuna papyracea, Lam. 



Eptiippium parviim papyraccum Anglicanam scu Polonicum, Chemnitz, Conchyl. Cabin., VIII, 1785, p. 



114, pi. 7<J, lig. 715. 

 Placuna papyracea, Lamahck, Hist. nat. d. anim. s. vert., VI, p. I, 18111, p. "^24. — éd. 2, 1836, VII, p. 27U. 



— — — Encyclop. metliod., pi. 174, fig. 2. 



— -- — Martini u. Chemnitz, Conchyl. Cabin., VII, 1. Abth., p. 6,5, pi. 5, fig. 2. 

 Placenta quadrangnla, Retzius, 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 (?), i.\ru Isl., Sorong, 

 Australia. 



Reeve, and J.E.Gray-' attribute mucli importance to the reciprocal length of 

 the two hinge-teeth, to their position with reference to each other, and to the angle 

 formed by them; in the case of young individuals these can bj' 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. 



Ephippiiim amilicanuni maximum, Chemnitz, Conchyl. Cabin., VIII, 178.5, p. 111. pi. 79, fig. 714. 



Anomia Sella, Ci.mei.in, Systema Naturae, ed. XIII, 179U, p. 334,5, No. 27. 



Placuna sella, — Lamarck, Hist. nat. d. anim. s. vert., VI, p. 1, p. 224. — éd. 2, VII, p. 270. 



' MoRCH, Catalog, conchyl. qiiæ reliq. com. de Yoldi, II, p. 63. The original specimen is in my 

 collection. 



- Spolia Zeylanica, vol. V, part XVII, Colombo, 1907, pp. 33-57. 

 ' Proc. of the Zool. Soc. London, XVI, 1848, p. 114. 



