Fragments of Natural History. 165 
‘This view of the subject has, I believe, borne the test of ex- 
amination, at least in our own country; for, so far as [ am ‘in- 
formed, it is sustained by every American naturalist who has had 
opportunities for careful and extensive observation. It holds true 
in respect to the following species found in the waters of the 
western states, the animals of which I have repeatedly dissected 
at different seasons of the year, and under various circumstances 
and conditions, without finding in any instance an exception— 
to wit: ; 
“= Esopus of Green. pres Rangianus. of Lea. 
alatus “ Say. sulcatus fr 
“  Japellus iced +: “  tenuissimust ‘  “. 
“ nasutus 74 “ ee zigzag} tt ec 
“  evatus fis. “  foliatus “* Hildreth. 
“* compressus “ Lea. “ orbiculatus . “ 
‘* capseformis  ‘“ ‘ parvus “ Barnes. 
Mecetvilas sects if “ tuberculatus “ = “ 
i iris “ it4 “ lut eolus * Tam. 
24%.2-irroratas?:) $$); ¥ 5 Seeman calceolag of eam 
‘“* leevissimus “© > Anodonta decora ~ 
‘< multiplicatus — “ “ . Ferussaciana “ “ 
“ multiradiatus “ rs plana i os 
se pileus* “cs te 
In several of the above species, the difference in the outlines a 
the shells in the two sexes is slight, and Bis escape the atten- 
tion of a hasty observer, yet it is pen ane > in 
whatever locality they are are found. _ 
There are certain ‘other species in peta iba sex is sat eitend. 
ed with any corresponding difference in the shell, at least so far 
as I have been able to discover. It may however yet be found 
upon further examination, that some minute difference has been 
overlooked. Of this character are the ee 
* The igs of Lea, and the personatus of Say, are the male and female of the 
same speci 
t The female is the U. velum of Say. 
t The U. donaciformis, iz the female of this species. 
§ The Margaritana deltoidea of Lea is the male, varied from the usual form and 
size by the peculiar influence of the waters of Mill Creek, near Cincinnati. 
