142 PROCEEDINGS OF THE ACADEMY OF 
two glass slides, wash away the particles of the broken shell in a 
few drops of water, still keeping the body of the animal on the 
slide; when clean, drop on it the caustic potash and boil it by 
holding the slide itself over the spirit lamp. 
On MOUNTING. 
For the purpose of examination, the jaw and lingual membrane 
may be simply mounted in water and covered with thin glass. 
One must be sure to spread out the lingual membrane, not have its 
upper side down, and it will be well to cut it transversely in 
several places, as the teeth are beautifully shown, and often stand 
detached, on the edges of the cut. 
For preservation for future study I hesitate to recommend any 
process, as I know of none which has been tried for a sufficiently 
long time. I have myself lost many specimens by imperfect mount- 
ing. Canada balsam, formerly used, ruins the membrane by render- 
ing it too transparent. The glycerine mounting fluids, now in use, 
certainly preserve a membrane for several years, but they have 
not been tried many years. 
ON THE JAW. 
The jaw and lingual membrane, having been mounted, must now 
be examined under the microscope. 
The jaw will be found to vary greatly in its characters in the 
different genera. It is either in one single piece (pl. XVL,, fig. 
1); in one single piece with an accessory quadrate piece attached 
to its upper margin; or in separate, detached pieces, free on their 
lower edges, usually soldered together into one single piece above 
(pl. XVI., fig. 13). It differs also in being with (pl. XVL., fig. 3), 
or without (fig. 6) a median beak-like projection to its cutting 
edge; also in its ends being more or less acuminated; but still 
more by the presence or absence of striz or rib-like processes 
on its anterior surface. When present, the ribs are found in 
every degree of development, passing quite across the jaw and 
denticulating one or both margins (pl. XVI., fig. 8), or only 
developed on the lower portion of the jaw, and creneilating the 
lower margin. The ribs are often almost obsolete, or represented 
by wrinkles or coarse striw. ‘They are present on the anterior 
