1895. 



PROCEEDINGS OF TUE NATIONAL M USEUM. 3<)1 



''O^^'^^.l^^^^^^t^fth^^^^^^ of the Shell and 



•mimal of many of the (Ufferent species, a luimber of con.-hologists, among 

 whom are Ratinesqiie/ Swaiuson,^ Agassiz^ and others, have attempted 

 to divide the genus into other genera and subgenera. These groups 

 are I believe, unworthy of any scientific standing on account ot the 

 abs'ohite blending of conchological characters in many cases and the 

 great variability of the soft parts. 



Iheriughas stated^ that the South American Unios, so far as Ins 

 knowledge goes, develop the embryos in the inner branchui; and not m 

 the outer Sutor has examined a number of the New Zealand Unios in 

 order to determine whether they were closely related anatomically t.» 

 those of South America, and he states^ that he found nearly all the 

 embryos in the inner branchi:^. Conchologically there is a very close 

 relation between the Unios of New Zealand, Australia, Tasmania and 

 South America, and there can be little doubt that the species throughout 

 have this anatomical peculiarity. In addition to this, the embryos of the 

 austral species seem to be mostly destitute of hooks, and von Ihermg 

 believes that they do not pass a part of their larval stage encysted on 

 the fins and gills of fishes, as do many of those of the northern hemi- 



^^ On' the other hand, the Unios of the northern hemisphere, so far as is 

 known, bear their embryos in the outer gills, and a considerable pro- 

 portion of them have hooks. Lea found these appendages m a large 

 luimber of embryos of Unios and Anodoutas, but absent in others In 

 those of U. hiteolus he found no hooks, but the nearly related L . radiatus 

 was furnished with four small ones, while in some specimens of Ano- 

 donta ovata, Lea. they were present and in others absent.' 



It is possible that hooks may be in some cases developed on the 

 embryo at one stage of its existence, and become broken off or obsolete 

 at another, as Lea found some examples in which they were imperfectly 

 developed. Some of the species of Europe luive been actually observed 

 attached to the gills and tins of ftshes by these hooks, and it is quite 

 probable that many of those of North America have similar habits.^ 

 During this period of attachment, which occupies two months or more, 

 the larvcc become encysted, and tlie organs develop, though the shell 

 does not increase greatly in size 



So far as I know, all the Unios of SouUi^ America, south ot the Isth- 



-TMor^:^l^s7;.;irBl^^^F^^ ^nn. G^n. des Sci. Phys., Brux., 



p. 291. 



-A Treatise on Malacology, 1840, p. 266. 



^'Archiv fiir Nat., 1852, p. 42. 



4\ew Zealand Jonrnal of Science, I, No. 4 (n. s.), p. 1..L, IS.tl. 



T'New Zealand Jonrnal of Science, I, No. 6 (u. s.), p. 2.-)0. 18!tl . , ^n 



•Lea fonnd hooks on the embryos of Umo peculians and ^- f'-'"l''' 'jl^'''^: 

 known Sonth American species. (Obs. , XII. pp. 26. 28.) He also states that Una « , - 

 tiplicatus, Lea, U. r„bu,hwsns, Lea, F. lleinianns, Lea. and I . .uI,rot,nulu., Lea, bear 

 the embryos in all four leaves of tlie branchiie. 



- Obs. on the Genus Uiiio, VI, p. 49, X, p. 89. 



