372 l*l^- ^' ^'' JA.MESOX ON THE [-^P''- 1*^5 



4. Ou the Identity and Distributiou ol" the Mother-ot- Pearl 

 Oysters ; with a Revision of the Subgenus Margaritifera. 

 By H. Lyster Jameson, B.A., Ph.D. 



[Received April 2, 1901.] 



(Text-figures 92-95.) 



ActiiJg u|)uu a suggestion made to me by Professor E. liay 

 LuDkest er, I have recently been engaged in i-earrauging tbe collection 

 of Maryaritifcrce in the 13ritisli Museum of Natural Hi.story, and in 

 revisiugand extendiug the series illustrating the commercial forms. 

 The nomenchiture of these forms has hitherto been iu a chaotic 

 state, and it has occurred to me that this revision of the genus 

 may be worth publication if only to prevent further confusion of 

 the common commercial forms by zoological and ecouoinic writers. 



The £ubgeuus Margaritifera (P. Browne = Mdeaijrina Lamarck) 

 is one of the three groups into which the genus Pferia (Scopoli = 

 Avicida Olivi) has been divided. 



It is distinguished from Fteria s. s. mainly by the small size or 

 complete absence of the posterior auricle or hiuge-coutinuatioo, and 

 by the fact that the longest dorso-ventral axis of the valves is 

 approximately at right angles to the hinge-line. 



In Fteria s. s. and Electroma Stoliczka (type ii". smarat/cUiui, 

 Reeve), on the other hand, the shell is oblique, i. e. the long axis 

 of the valves is directed obliquely backwards. 



Electroma is distinguished from Pteria s. s. by the shortness of 

 its hinge and the absence of tbe posterior auricle. 



Such species as Margaritifera vulgaris and M. panasesce, together 

 with certain Pteria^ and Electroma^, tend in many ways to bridge 

 over the gaps between these three subgenera. 



G-enus Pteeia 8copob, 1777, p. 397 : type Mytilas hirundo Linu. 

 =Avicida Olivi, 1792, p. 125. 



Subgenus MAKGAEiiirEKA P. Browne, 175G, p. 412. 

 (Non biuom. : type ill. radiata Leach ; Jamaica.) 



= Margaritifera Humphrey, 1797 (ex parte), p. 44: type M.fim- 

 hriata (notdescr.) ( ? = ili. radiata Leach) ; W. Indies. Apud 

 Da Costa, 1776. 



= Margaritophora Megerle von Miihlfeld, 1811, p. ti6 : type 

 M. communis =M. margaritifera Linnaeus. 



= Meleaffrina Lamarck, 1812, p. i04 ; 1819, p. 150: type M. mar. 

 garitifera Linnaeus. 



= Margarita Leach, 1814, vol. i. p. 107: type M. sinensis Leach 

 = M. margaritifera Linnaeus ; China. 



= Perlamater Schumacher, 1817, p. 107 : type P. i'»Z(/rtm Schu- 

 macher. 



The species of Margaritifera are difficult to separate from one 



