161 



lamellar teeth, with the exception, however, of Iridma of Lamarck, 

 which has an elongated, linear, crenulated hinge, and was placed by 

 Brugui^res in Anodonta, to which, indeed, it is intimately linked 

 by the I. nihtica. Ferussac, in his Tableaux Syst., included all 

 the genera of this family in four, viz., Anodonta, Hyria, Unio, 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 Geneva, affirms that he observed, in some individ- 

 uals of the Unio pictorum, the existence of spermatic animalculse, 

 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 



