W. Stimpson on the so-called Melanians of N. America. 49 
are even species in which the margin of the branchial siphon 
(perhaps the most important part of the mantle-edge) is t 
re are, however, 
plenty of Cerithia in which the mantle is simple-edged, and these 
animals have much more intimate relations to Melania than have 
most of the genera included in “Fam. 1, Melaniidee.” 
Dr. Lea, in the ninth volume of his “Observations on the 
genus Unio,” etc. and in minor papers published previously, 
recognizing the importance of subdividing the numerically enor- 
mous collection of forms commonly included under the “genus 
Melania,” has very properly proposed distinct generic names for 
the several groups of species which are indicated by the con- 
chological characters. Whether these characters are truly the 
most important that can be discovered, we do not pretend to de- 
cide; but there is no doubt that distinct types exist, around 
which the species may be grouped, in accordance with their 
affinities. That these genera run into each other, is no argument 
against the necessity of their acceptance, for the ‘same may be 
Said of very many genera in all classes of the animal kingdom, 
especially when we study the remains of their representatives 
In geological times. Dr. Lea, has, however, erroneously included 
the genus Amnicola in his family Melaniide.” That —_ be- 
longs to an entirely different group, near! y allied to the Rissoidee, 
(if not, indeed, belonging to that family) ; the intromittent 
organ in the male being distinctly exserted. 
The next-published observations upon the soft parts of Amer- 
describes J. subu- 
terpreted its nature, and considered it a specific character, Thus 
; MS z ‘ 
i pais genus Unio, etc., vol. ix, (1862), p. 40. 
ie Pecoasiigs ot tes Philadelphia Acad. Nat. Sci. for 1862, p. 588. 
Am. Jour. Sct.—Szconp Szrms, VoL. XXXVII, No. 112—Juxr, 1864. 
rg 
