A MANUAL OF AMERICAN LAND SHELLS. 45 



the method usually employed is puttiug the whole buccal mass iu a 

 watch crystal full of a strong solution of caustic potash. Allowing it 

 to remain for several hours, the potash will destroy all of the buccal 

 mass, and leave the jaw and lingual membrane perfectly clean aixd 

 ready for examination. They remain attached if the solution is not too 

 strong, showing a connection between the two. They must be well 

 rinsed in clean water, in another watch crystal, before examination. 

 Another more expeditious process is to place the whole buccal mass in 

 a test-tube with the solution of potash, and boil it for a few seconds 

 over a spirit lamp. Pouring the contents of the test-tube into a watch 

 crystal, the lingual membrane attached to the jaw will be readily seen 

 by a pocket lens. If the species be very small, as Patula striatella for 

 instance, its whole body may be thrown into the solution. Still more 

 minute species, as Zonites milium for instance, may be treated in this 

 way: Crush the whole shell between 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. 



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 the glycerine mounting fluids sold 

 by the opticians will be found useful, though they have the great dis- 

 advantage of deliquescing in warm weather. 



The jaw and lingual membrane, having been mounted, nuist now be 

 examined under the microscoije. 



The jaw will be found to vary greatly in its characters in the different 

 genera. It is either in one single piece {Holognatha) ; in one single 

 piece with an accessory quadrate piece attached to its upper margin 

 {Elasmognatlia) ; or iu separate, detached pieces, free on their lower 

 edges, usually soldered together into one single piece above ( Goniognatha). 

 It differs also in being with or without 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 i^rocesses 

 on its anterior surface. When present, the ribs are found iu every de- 

 gree Of development, passing quite across the jaw and denticulating 

 one or both margins, or only developed on the lower portion of the jaw 



