AMI'ULLA'IIIA, a genus of Fresh-Water Spiral Univalve Shells, which are found in the riven, and ponds of India, Africa, and South America. They are of a globular or rather depressed form, are covered with a thick olive or black periostreca, and often banded. Their mouth is ovate, with the lips complete all round, and often slightly thickened or reflexed. The animals are somewhat similar to the Common Pond Snail (Paludina), but they have the front of the head nicked and furnished with two slight conical horn-like processes; and they have long slender tentacles, with the •eyes placed on small policies at their outer base : these home and the tentacles often contract into a spiral form. But the groat peculiarity of these animals is, that, unlike all other mellnacoua animals with comb-like gills, they have a large bag, which opens beneath, placed on the aide of the respiratory cavity, which they probably can fill with water ; and it is this structure which most likely gives them the power of living for a long time out of water, specimens having been brought from Egypt to Paris alive, by only packing them in a little sawdust. Their operenlum
is formed of concentric rings with the nucleus nearly in the centre; in the species which come from India, this part is generally but in those of America and Africa it is always horny. The Indian species lay globular pale-green eggs about the size of small peas, which are placed in clustera on sticks and other things in the ditches; the eggs when dry form most beautiful objects,. Some of the African species are reversed, or have the whorls of the shell turned from the right to the left, and these have been separated into a genus, under the name of Leniaves, on this account. It has been generally supposed by the geologist, that all the species of this genus are purely fresh water, but the large Egyptian species, A. orate, discovered by Olivier in Egypt, lives in Lake Mareotis, where the water is salt ; therefore there is no proof that some of the fossil species are not marine.