1882. ] PROF. W. H. FLOWER ON THE EDENTATA. 359 
Cuvier’s order included the Ornithorhynchus and Echidna, animals 
of which the structure was then imperfectly known, but which are 
now by almost universal consent removed to an altogether different 
section of the class. Otherwise its limits are those now adopted. 
The name Ldentata, moreover, is now so generally used, and its 
meaning so well understood as a conventional term, that it would be 
very undesirable to substitute any other for it. In fact similar reasons 
might be given for ceasing to use nearly all the current ordinal desig- 
nations of mammals. It might be equally well objected that all 
the Carnivora are not flesh-eaters, many of the Marsupialia have 
not pouches, and so forth. 
The few common characters by which the Edentata are associated 
are too well known to need repetition. The principal one is the 
absence of any trace of the typical heterodont and diphyodont den- 
tition, found in a more or less modified form in all other placental 
mammals’. The one genus Tatusia presents a startling exception, 
in the presence of a set of milk-teeth, with (according to Burmeister) 
distinct rootsimplanted in separate alveoli, and (according toC. Tomes) 
distinct enamel-organs, if not enamel. This is one of the most im- 
portant facts bearing upon the evolution of the Edentates yet dis- 
covered, though its full signification is not yet evident. 
It is highly probable that most, if not all, of the existing Eden- 
tates are the very much differentiated representatives of a large 
group, the greater number of which are uow extinct, and which 
have become so without ever attaining a high grade of organization. 
The great diversity of structure, the high degree of specialization 
to which many have attained, the paucity of species and even of 
individuals, their limited area of distribution, and their small size 
compared with known extinct forms, all show that they belong to 
an ancient and waning race, the members of which still hold their 
own either by the remoteness and seclusion of their dwelling-places, 
their remarkable adaptation of structure to special conditions of life, 
or by aid of the peculiar defensive armature with which they are 
invested. Their former history can, however, only be surmised, 
rather than read, at present ; for though we have ample evidence of 
the abundance and superior magnitude of certain forms in the most 
recent and post-Tertiary geological age, and in one part of the world, 
beyond that time (7. e. in the true Tertiary period), and in other parts 
of the world than America, their fossil remains hitherto discovered 
are only fragmentary, giving a most imperfect idea of their actual 
condition, as well as affording no indications that serve to connect 
them with certainty to any other branch of the class. 
The existing Edentates readily group themselves into five distinct 
families, of the limits of which there is no reasonable doubt. These 
are :—1. The Brapypoprp4&, containing two genera, Bradypus and 
Cholepus. 2. The MyrMEcoPHAGID4, containing three distinct modi- 
fications, worthy of generic rank—Myrmecophaga, Tamandua, and 
* The Cetacea are possible exceptions ; but embryological and palzontological 
researches appear to show that their dentition may be derived from the ordinary 
mammalian type. 
