Page:Land Mollusca of North America (north of Mexico) Vol. I Part 1 i-276.pdf/13

Rh Gerontic. Old age, often expressed by irregular roughening of sculpture, thickening of the lip, and, finally, more or less marked loosening of the coil, as in page 525, Figure 343: 1-14, representing an extreme instance.

Each of these stages may be subdivided by use of the prefixes ana-, meta-, para-. Thus ananeanic signifies an early neanic substage; metaneanic, mid-neanic; and paraneanic, a late neanic substage, or almost full grown.

The collector should take a few young shells, as the sculpture of the embryonic stage is often so delicate that it is frequently imperfect or entirely lost from the apices of adults.

Types.—The term type, which has served without ambiguity for many years, seems to me preferable to "holotype" which is equivalent in meaning, both referring to the specimen originally described of a species or subspecies. Reference to the museum number and the location of type specimens is included in the Distribution paragraph, immediately following the type locality, these abbreviations being used:

Names of other institutions and collections are written in full.

When an author specifies "cotypes," or when there are several examples in his original lot, neither specified as type, one specimen has often been taken as a "lectotype". In a few other cases, where the type material has been lost, a "neotype" has been selected. "Paratypes" are specimens other than the type, which were before the author of a species and more or less directly referred to in the original account.

References.—To save space in a work already too long, the references to literature have been restricted to those thought to be most useful. Many European references to the older species, though useful in their day, have now only a minor historic interest; those concerned with them are referred to the works of W. G. Binney and L. Pfeiffer. As W. G. Binney's several monographs of 1869, 1878 and 1885 contain substantially the same descriptive matter and figures of shells, reference has usually been made only to the Terrestrial Mollusks V, 1878, as this contains Binney's anatomical work, and reprints of the exquisite figures of Volume III.

In only special cases references are given to Tryon's Monograph of the Terrestrial Mollusca of the United States, in American Journal of Conchology II-IV, 1866-1868; and to his work in the Manual of Conchology I-IV, 1885-1888. Several lists, such as the Classified Catalogue published in Nautilus XI, XII, 1897-8, are also omitted. These