Shasthancottah.—There are two villages of this name, one situated on the backwater near Quilon (coast of Travancore), the other about three miles inland on a large freshwater lake. This lake, which does not communicate with the backwater, occupies a narrow winding rift several miles in length at a considerable depth below the surrounding country. Its bottom is muddy and it contains few water-plants, although in some places the water-plants that do exist are matted together to form floating islands on which trees and bushes grow. The fauna, at any rate as regards mollusca and microscopic organisms, is remarkably poor, but two species of polyzoa (Fredericella indica and Plumatella fruticosa) and one of sponge (Trochospongilla pennsylvanica) grow in considerable abundance although not in great luxuriance.
The Himalayas.
Bhim Tal[[H]] is a lake situated at an altitude of 4500 feet in that part of the Western Himalayas known as Kumaon, near the plains. It has a superficial area of several square miles, and is deep in the middle. Its bottom and banks are for the most part muddy. Little is known of its fauna, but two polyzoa (Plumatella allmani and Lophopodella carteri) and the gemmules of two sponges (Spongilla carteri and Ephydatia meyeni) have been found in it.
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Nomenclature and Terminology.
The subject of nomenclature may be considered under four heads:—(I.) the general terminology of the various kinds of groups of individuals into which organisms must be divided; (II.) the general nomenclature of specimens belonging to particular categories, such as types, co-types, etc.; (III.) the nomenclature that depends on such questions as that of "priority"; and (IV.) the special terminology peculiar to the different groups. The special terminology peculiar to the different groups is dealt with in the separate introductions to each of the three parts of this volume.
(I.)
No group of animals offers greater difficulty than the sponges, hydroids, and polyzoa (and especially the freshwater representatives of these three groups) as regards the question "What is a species?" and the kindred questions, "What is a subspecies?" "What is a variety?" and "What is a phase?" Genera can often be left to look after themselves, but the specific and kindred questions are answered in so many different ways, if they are even considered, by different systematists, especially as regards the groups described in this volume, that I feel it necessary to state concisely my own answers to these questions, not for the guidance of other zoologists but merely to render intelligible the system of classification here adopted. The following definitions should therefore be considered in estimating the value of "species," etc., referred to in the following pages.
Species.—A group of individuals differing in constant characters of a definite nature and of systematic[[I]] importance from all others in the same genus.
Subspecies.—An isolated or local race, the individuals of which differ from others included in the same species in characters that are constant but either somewhat indefinite or else of little systematic importance.