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clature is not now studied, in the name of formic acid. This acid was first obtained from the red ant, (Formica rufa,} and should have been culled formicic acid.

There is one role, which seems to be well established, and deserves particular notice, as it appears to conflict with that laid down above. In such words as Distoma and Leptothrix, the last components stoma and thrix are need in the nominative case, which does not here show the true stem. The reason is that no termination has been added in these cases: when, however, that is done, the true stem ought to appear, as in Distomatidæ (erroneously written Distomidæ) and Leptotrichum. It is, indeed, impossible to insist absolutely upon obedience to these rules; euphony must be consulted, and will occasionally give the preference to the loss correct form. Moreover, the ancients themselves sometimes failed to observe their own precedents. Thus from lapis, (stem, lapiid-,) "a stone," they obtained lapicida, "a stone-cutter," after which Linnæus named Helix lapicida; but from those who know what it ought to be it requires an effort not to write H. lapidicida, as has been in fact sometimes unconsciously done.

It may be useful to give an epitome of the chief Latin terminations, with the rules concerning them, so far as they concern our purpose. The genitive case, which answers to our possessive case, and means "of (a thing,)" is given as well as the nominative, because it is often required, as will be seen further on. In Latin, nouns are divided into five classes, called declensions, but only the first three of these are important to us, words belonging to the others being very rarely met with. Those belonging to the first declension and in -a and -e, and are feminine, or in -es, and are masculine; those of the second in -us and -er, and are masculine, {except names of trees in -us, as Fagus, which are always feminine,^[1]) or in -um, and are neuter. More than two-thirds of the nouns used in scientific nomenclature belong to these declensions; these are, therefore, the most important, and are also the easiest to understand.

The method of applying this and the following table is as follows:—Take away from the word the letters given in the first column; what

remains is the stem, and to it must be added the respective letters given in the other columns. There is one exception; in words ending in -er, the r forms an essential part of the stem. As examples we may take fungus, a mushroom, fungi, of a mushroom, fungi, mushrooms, fungorum, of mushrooms, fung- being the stem; but in liber, a hook, libr- is