wiih a revision of thè Limnwìdce of Authors. 359 
is thè type. In so small an animai it might readily he over- 
looked or even be entirely absent. 
It is to be hoped that thè numerous observers "who are fur- 
nished with microscopes will avail thernselves of thè riches 
which lie hidden in every brook and pool. The dentition and 
anatomy of our native species of Physa, Limnoea, Planorbis, 
as well as thè Ywiparidce and thè Strepomatidce are almost 
entirely unkuown. 
The ribbon may be most easily obtained by boiling thè ani- 
mai in a test tube over a spirit lamp, in a solution of caustic 
potash. It can easily be found by pouring thè contents of thè 
tube into a smooth white saucer, or a deep watch-glass. The 
Shell from which thè animai was extracted should always be 
preserved, and thè ribbon mounted, when praeticable. 
Great care is needed when inexperienced in such work, par- 
ticularly when working with a low power, not to mistake thè 
outline of thè base of inserti on of thè tooth for its cusp. Tlie 
lattei’ is almost always transparent, and nearly invisible when 
compared with thè base, which is usually dark yellow. 
A good pian is, when specimens are plenty, to break up thè 
ribbon after a dose examination of it in thè entire state. In 
this way thè outlines of thè edges of thè cusps are more easily 
made out. Drawings, no matter how rude, should be made on 
thè instant, and repeated until thè entire accuracy of thè out- 
lines is beyond dispute. Some assistance may be obtained in 
such work from photography, which, uncorrected by a trained 
eye, is, however, very liable to mislead. The extreme ante- 
rior teeth are usually mudi worn and broken by use, and thè 
extreme posterior ones are immature and not fully shaped. 
The middle of thè odontophore atfords thè best examples. 
The jaws are destructible in potash and should be examined 
in situ, by placing thè animai on a needle stuck into a cork, 
which should be lixed on thè stand of thè microscope, and light 
should be condensed by a bull’s-eye lens on thè part of thè 
animai which it is desired to observe ; but not too strongly, or 
it will be burned or dried up. 
