241 



REVIEW OF THE GENUS PLECOTREMA. 



By E. R. Sykes, B.A., F.Z.S. 



The generic synonymy of this rather artificial genus of TnoUuscs 

 appears to be as follows : — 



1854. Flecotrema,^ H. and A. Adams, Proc. Zool. Soc. 1853, p. 120. 



1855. ,, ,, ,, Genera of Recent Mollusca, 



vol. ii. p. 240. 



1856. ,, Pfeiffer, Mon. Auric, p. 99. 



1857. ,, ,, Auric. Mus. Brit., p. 75. 



1876. ,, „ Mon. Auric. (Mon Pneum. Viv. Supp.), 



p. 343. 

 1837. ? Lirator, Beck, Index Moll., p. 103. 



1846. Lmnodonta, Philippi, Zeitsch. fiir Malak., 98. 



1847. Laimodonta, Bronn, Preissver. Ausl. Konch. Mus. Heidel., 



iv. p. 4. 

 'i Laimodonta, Nuttall MS. {non H. and A. Adams). 



None of the names proposed by Beck, Philippi, or Bronn can, in my 

 opinion, be used ; the first, since it is unidentifiable, and the others 

 because they were not described. The type, as proposed by Messrs. 

 Adams, is P. typicum, H. and A. Adams. One feature on which these 

 authors laid especial stress when founding the genus, namely, that 

 single columellar plait is bifid, does not appear to be even specifically 

 constant, but it is so convenient a group that it will probably, for the 

 present, continue to be used. The recent distribution appears to be 

 confined to Fischer's Indo-Pacific province. The genus first appears 

 in the Calcaire Grossier de Mons (the equivalent of our lowermost 

 Eocene) ; and it is interesting to note that the oldest species are smooth 

 shells, while in the Miocene the sculptured species make their appear- 

 ance, and at the present time hardly a recent form is without 

 well-marked sculpture. 



Our only knowledge of the animal appears to be a description of its 

 external appearance by Harper Pease. ^ 



Considerable difficulty has been caused in identifying the species owing 

 to the brevity of the Messrs. Adams' original descriptions, as well as by 

 the lack of figures and dimensions. Pfeiffer, in his works, appears to 

 have elaborated the Messrs. Adams' descriptions from the specimens in 

 the Cuming Collection in the British Museum — from which their 

 species were originally described — without in all cases verifying the 

 tablets to see that they were correctly named. I have not tried to 



^ Derived from ttk4kos, rpriixa ; the ueuter termiuation has therefore beeu used. 

 2 Proc. Zool. Soc. 1869, p. 59. 



