524 



Phylum Mollusca 



it may be obtained in most places the year around. The lettuce may 

 be kept for weeks in a mechanical refrigerator in a covered tin can. Use, 

 except in the cases discussed subsequently, only the leafy part of the 

 lettuce whether bleached or unbleached, avoiding the central vascular, 

 thick part of the leaf as well as any part that has been bruised. The 

 lettuce in its preparation for the aquarium should be torn with the 

 fingers, avoiding excessive pressure and the use of the thumb nail as a 

 punch. 



Calcium carbonate. In addition to the foods mentioned above, cal- 

 cium carbonate not only is desirable but seems almost indispensible. 

 It is not only eaten by the snails but it serves also to regulate the acidity 

 of the water; however, it is of no value for this purpose in an over- 

 stocked aquarium or one in which there is an excessive amount of decay- 

 ing organic material. Calcium carbonate in the form of crushed lime 

 rock or of precipitated chalk is of no value in snail culture, since these 

 forms appear to be too finely divided and cause the snails to produce 

 a superabundance of slime. Calcium carbonate comparable to "Baker's 

 Analyzed" (product of the J. T. Baker Chemical Co.) is the form most 

 suitable for both terrestrial and aquatic snails. 



PREPARATION OF THE HABITAT 



For a small number of snails an evaporating dish 9 inches in diameter 

 and 3 inches high is suitable; this should be filled with approximately 

 2,000 cc. of water or to within about Yi inch of the top. To the water 

 should then be added about one gram of calcium carbonate; most of the 

 carbonate should be piled up near the center with a thin film spreading 

 over most of the bottom of the aquarium. This may be accomplished by 

 dropping the calcium carbonate from a piece of paper held about 3 

 inches above the surface of the water. Dry leaves in an amount of leaf 

 area equal to the area of the bottom of the aquarium are introduced; 

 the leaves should be piled up so as to cover only about a third of the 

 bottom. After the addition of the snails and a small amount of lettuce 

 the aquarium should be covered with a glass plate; the cover need not 

 be propped up for air circulation unless the snails crawl out of the 

 water and carry with them enough water to "seal" the cover. 



An aquarium of this size will support about 12 Fossaria modicella, 6 

 Helisoma trivolvis, or 8 Pseudosuccinea columella for months; eggs or 

 young snails should be removed promptly. 



Species of Fossaria, Helisoma, Planorbula, Gyraulus, Physa, Stag- 

 nicola, Lymnaea, and Pseudosuccinea have been raised without difficulty 

 by using this method. It should be noted, however, that Fossaria 

 modicella, F. m. rustica, and Pseudosuccinea columella may normally 

 spend much of their time out of water ; this, however, should not occa- 



