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lamellar teeth, with the exception, however, of Iridina of Lamarck, 
which has an elongated, linear, crennlated hinge, and was placed by 
Bruguitires in Anodonta, to which, indeed, it is intimately linked 
by the I. nilotica. Ferussac, in his Tableaux Syst., included all 
the genera of this family in four, viz., Anodonta, Uyria^ Unto, and 
Castalia. Sowerby has since proposed to retain Unio only, and, as 
Ferussac had already done, to consider the other genera as sub- 
genera. 
Blainville describes the animal nearly thus : Body large, thick, 
more or less oval ; mantle thickened on the margin, simple or 
fringed, and excepting on the back, open all around ; anus oval, 
distinct ; a kind of small incomplete tube, furnished with two 
ranges of cirri, for the respiratory cavity ] foot very large, com- 
pressed, lamelliform. 
The principal naturalists and anatomists have been decidedly of 
opinion that the animals of this family are hermaphrodites ; but 
Mr. Prevost, of Gleneva, affirms that he observed, in some individ- 
uals of the Unio pictorunij the existence of spermatic animalculae, 
which he could not perceive in those which contained eggs. He 
therefore inferred that the sexes were distinct. This led Blainville 
to a re-examination of the subject: he dissected about forty indi- 
viduals of the genera Unio and Anodonta, without discovering any 
indications that could lead him to suppose the existence of the male 
sex ; still, however, he is in doubt, and we are very much inclined 
to believe, with Ferussac, that Prevost may be right, but that more 
observations and observers are required fully to establish this dis- 
puted point, although Baer has gone far towards even this object. 
Treviranus also made some interesting observations on this subject, 
an account of which he published in the Zeitsch. fur Physiol, in 
1824. He was of the opinion that the same organ produced both 
the ova and the fecundating fluid. He, however, remarks that 
he found, at the season of excluding their eggs, many that were 
entirely destitute of them. 
Some naturalists have changed the designation of this genus to 
Anodon, as being more rigidly correct. 
Anodonta suborbiculata. — Specific character. Suborbicu= 
lar, a little winged. 
Desc. Ovate-orbicular, rather compressed ; pale olivaceous 
tinted with flesh color ; with very slender, almost capillary, and 
