REPOET 



UPON THE 



ANATOMY OF PLACUNA PLACENTA, 



WITH 



NOTES UPON ITS DISTRIBUTION AND 

 ECONOMIC USES, 



BY 



JAMES HORNELL, F.L.S., 



Superintendent of Pearl and Chank Fisheries, Madras. 



[With Five Plates aud Two Text Figures.] 



THE anatomy of the window-pane oyster (Placuna placenta, L.) lias never been 

 worked out, and references to it in the literature of the Lamellibranchs are scarce. The 

 literature of the genus Anomia, to which Placuna is most nearly related, is likewise 

 scanty. The principal is by F. J. H. Lacaze Duthiers, who published in 1854 a 

 " Memoire sur 1'organisation de 1'Anomie." l 



A short critique of this by Pelseneer appeared in 189 1, 2 in which he amplified and 

 corrected certain points, while Sassi 3 has contributed an important paper dealing 

 principally with the renal system. Von Ihering 4 and Morse 5 have also treated of 

 Anomia, and occasional references to this genus are to be found scattered through works 

 dealing with the morphology of molluscs, but Placuna, though well known by reason 

 of the minor economic uses which it subserves, has hitherto failed to attract that 

 attention from the morphological standpoint which it undoubtedly deserves ; the 

 peculiar asymmetry exhibited by many of its organs possesses extreme interest when 

 considered in conjunction with habits arid habitat, while the strange mingling of primi- 

 tive or archaic characters with others of extreme modification and specialisation has 

 much that will repay careful study. 



1 Ann. des sci. nat., Zoologie, ser. 4, tome ii. 1854. 



2 "Contribution a 1'etude des Lamellibranches " (Archiv. de Biologie, tome xi. 1891). 



3 "Zur Anatomic von Anomia ephippium " (Arb. Zool. Iitnt. Wien, xv. Heft 1, 1903). 



4 "Ueber Anomia," etc. (Zeitch. fur Wiss. Zool., tome xxx., vol. supplem., 1878). 



5 "On the Relations of Anomia" (Proc. Boston Soc. Nat. Hist., vol. xiv. 1871). 



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