114 Mr. Barnes on the Genera Unio and Alasmodonta. 
themselves buried in the mud, having their beaks turned 
downward, If he means by this that they are usually 
concealed, or that they lie on their beaks; we remark 
that, s it regards those of our country, such is not the fact. 
In wonter they may bury themselves, but in summer we 
have found them, generally, when at rest, standing with 
the posterior side inserted obliquely, and the hinge margin 
the anterior slope, and a small portion of the basal edge ex- 
serted. Even when they sink below the surface the place of 
their retreat is conspicuous. In streams which have a rough 
ottom and rapid current, they choose the narrow crevi- 
ces between the stones or under the edges of rocks, and 
thus defend themselves from injury. e have never found 
a live . nio on its back, or on what M. Lamarck and his 
followers would call the base. 
While standing in the position above described, they have 
the anterior side slightly gaping, but on being touched they 
strong resemblance to the eyes of a large animal. Deter- 
ville says “they have been observed to live for several 
months of the summer in clay too hard to be cut by the 
hoe, and with but momentary showers to refreshthem,.” This, 
if it be a fact, must rest, for the present, on his authority ; as 
we know of no one who has confirmed it by observation. 
We know but little concerning the generation and - 
agation of the species of Molluscous animals that inhabit 
these shells, They are generally supposed to be hermaph- 
rodite per se, If they are really and absolutely so, the num- 
ber of species must be exceedingly great. M. Lamarck 
supposes that they are propagated by means of a fecunda- 
ting fluid emitted into the water. If so, they must be male 
and female. What reason he has for this supposition, we 
are not informed, but if it be admitted, it will readily ac- 
count for the numerous varieties of these animals, and it 
will show also that they are merely varieties, and not dif- 
ferent species, that is, they will prove to be the “ common 
* Ils se tiennent enfoncés dans la vase, ayant leur crochets tournés en bas.” 
—Lam. An. S, Vertebres, Voi. V1. page 70, 
