,374 MONOTKBMA.IA. 



cavity. There are no isolated palatal vacuities, although the median 

 line of the palate posteriorly is often more or less imperfect ; there 

 are also as a rule large condyloid vacuities. Auditory hullse are 

 never developed. • 



True functional teeth are now whoUy absent in the Order ; but 

 as, in the young of the OmitJiorJiynchidce, rudimentary teeth are 

 developed beneath the gum, only to be reabsorbed before being out, 

 it is evident that the ancestors of the Monotremes had functional 

 teeth at no very distant date. 



In the OmithorJiyncMdm the teeth have been replaced, so far as 

 function is concerned, by horny plates developed from the palate- 

 ridges, whUe in the Echidnidce, just as in the ant-eating Edentates, 

 they have been lost without leaving any functional successors. 



Owing to the very numerous accounts of the anatomy and embry- 

 ology of the Monotremes already existing, it is thought better that 

 no attempt should here be made to describe in detail the many 

 important and essential characteristics of the, members of the group ; , 

 but fairly foU bibliographies of the literature of the subject are 

 given below. For the same reason the references to the anatomical 

 and embryological papers have been separated from the ordinary 

 systematic synonyms, and placed together under the headings of 

 the families to which they belong. 



Synopsis of the Families, Genera, and Species. f 



I. EXTEEKTAL ChAKACIEES. 



A. Beak cylindrical. Fur mixed with 



spines. Toes not webbed I. EcMdnldSB, p. 375. 



a. Claws 6 — 5. Beak comparatively 



short 1. Echidna, p. 377. 



a^. Head and body about 350 to 450 

 miUim. Tip of snout to eye 

 about 40 to 55 millim 1. E. aculeata, p. 377. 



b. Olaws normally 3 — 3. Beat very 



long, curved downwards 2. Peoechidna, p. 382. 



b^. Head and body about 450 to 600 

 millim. Tip of snout to eye 

 about 90 to 130 millim 1. P. bruijnii, p. 383. 



B. Beak broad and flattened. Fur with- 

 out spines. Toes webbed II. OrnithorhvnohidsB, p. 385. 



Claws 5 — 5 1. Oenithoehtnchus, p. 887. 



c\ Head, body, and tail about 400 to 



650 mOlim. in fength 1. 0. anatinm, p. 388. 



c. 



II. Ckanial Ghaeaotees. 



A. Muzzle slender, premaxillse not ex- 

 panded in front. No dental organs 

 of any sort present I. EchldnldSB, p. 375. 



