456 MICHIGAN SURVEY, 1905. 



brane. These can be removed by fine scissors or knives from the buccal 

 mass in the larger species, but in the smaller species, the method usually 

 employed, is putting the whole buccal mass in 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 lin- 

 gual membrane perfectly clean and ready for examination. 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 tube into a watch crystal, the lin- 

 gual membrane attached to the jaw will be readily seen by a pocket lens. 

 If the species be small, as Pyramidula striatella, for instance, its whole body 

 may be thrown into the solution. Still more minute species, as Zonitoides 

 milium, for instance, may be treated in this way; crush the whole shell 

 between two glass slides; wash the particles of 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 dow^n, and it 

 is well to cut it transversely in several places, as the teeth are beautifully 

 shown and often stand detached on the edges of the cut. 



'Tor preservation for future study, the glycerine preparations sold by 

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

 tages of deliquescing in w^arm weather." * 



The radula may also be mounted in Canada balsam. In this case they 

 should be stained with carmine or chromic acid, as otherwise the specimen 

 will in time become transparent. 



' VI. 

 CLASSIFICATION. 



ORDER PULMONATA. 



Animal naked or covered with shell, inoperculate, terrestrial, fluviatile or 

 marine, breathing the air by means of a lung with vascular walls and a con- 

 tractile orifice. Both sexes are united in each individual, but the genital 

 orifices are either contiguous and opening into a common duct, or sepa- 

 rated. Jaw single or composed of three pieces; never of two symmetrical 

 pieces. Radula with very numerous teeth in each row. 



Shell of variable shape, holostomus. 



The Pulmonata are divided into two sub-orders according to the position 

 of the eyes and the character of the tentacles, viz.: 



I. Eyes placed at the extremity of retractile tentacles. . Stylommatophora. 



II. Eyes placed on the base of contractile tentacles .... Basommatophora. 

 The Stylommatophora are as a rule terrestrial in their habits, while the 



Basommatophora are amphibious or aquatic. 



The Stylommatophora are again divided according to the position of the 

 genital orifices. 



* W. G. Binney, Man. Am. Land Shells, p. 44. 



For full instructions in regard to the preparation of the radulae of the minute species, see Beechcr, 

 Journal N. Y. Microscopical Society, 1888, p. 7. . 



