JOURNAL AND PROCEEDINGS, 799 
sive, the dealer’s price averaging from $15 to $20, according to 
size, state of preservation, etc. So many men are now engaged 
in dredging that it may be reductions have been made recently 
which are unknown to me. 
THE MACTRID-. 
The writer retains a clear recollection of the olden kneading 
trough used in the country districts in Ireland formerly (and it 
may be still) for the purpose of making the home-made bread for 
the family. The Lutraria, or otter shell of Lamark, so closely 
resembled it in shape, that one need not feel surprised that it 
may have suggested the name it bears. I think I am ac- 
quainted with only two members of the family, Mactra Stultorum 
and Lutraria Oblonga, both inhabitants of British waters, neither 
of which I recognize in the Museum collection here. Another 
specimen of shell found on the coast of New Orleans, named 
Gnathodon Cuneatuse by Gray, with a shell of considerable thick- 
ness for the size represented, I have not seen; perhaps they are 
not by any means an attractive class, and, although there are 
sixty or more species widely distributed—but a majority in the 
tropics—the dealers seldom have many for sale. They bury 
themselves a little below the surface in sand or mud. Lyell 
mentions a curious fact regarding the Gnathodon, viz :—The 
road from New Orleans to Point Chartrain, (six miles), is made 
of these shells, procured from the east-side of the lake where 
there is a mound of them a mile long, fifteen feet high, twenty 
to sixty feet wide, and in places about twenty feet above the 
lake level ; banks of dead shells are found twenty miles inland. 
Mobile is built on one of these shell banks. A species has 
been found in the Miocene of the States, and thirty species of 
Mactia are known to occur in Mesozose rocks, (Lias) and 
upwards. The marking called the pallial impression of a shell 
represents where the border of the mantle was situated, and 
when a sinus or bay is noticeable it proved the animal (Mollusc) 
possessed retractile syphons. A close relatioaship may be 
noticed in families now separated by Conchologists or dealers, 
by comparing the internal markings of various groups. The 
