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 (pi. XVI., fig. 

 1) ; in one single piece with an accessoiy 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 

 (pi. XVI., fig. 13). It differs also in being with (pi. XVI., fig. 3), 

 or without (fig. 0) 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 striae 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 (pi. XVI., fig. 8), or only 

 developed on the lower portion of the jaw, and crenellating the 

 lower margin. The ribs are often almost obsolete, or represented 

 by wrinkles or coarse stria?. They are present on the anterior 



