MAMMALIA. 



e.co 



Sub-class PROTOTHERIA (Syn. ORNITHODELPHIA), 

 Orders Monotremata and Allotheria. 



The Monotremes include the duckmole (Ornithorhynchus 

 anatinns], the spiny ant-eater (Echidna aculeata), and a 



third form resembling Echidna, 

 but often referred to a distinct 

 genus as Proechidna. These are 

 the lowest Mammals, very differ- 

 ent from all the rest, and they 

 exhibit affinities with Sauropsida, 

 -co. and perhaps even with Am- 

 phibia. It need hardly be said 

 that they have no special affinities 

 with Birds. 



The duckmole is found in the 



1- IG> 35 i. Pectoral girdle of rivers of Australia and Tasmania ; 

 Echidna. From Edinburgh Echidna, in Australia, Tasmania, 



Museum of Science and Art. and Ngw Gu i nea . p r0 echidna in 



New Guinea. 



In Ornithorhynchus the skin 



is covered with soft fur ; in 



Echidna and Proechidna there are spines among the hairs. 

 The mammary glands in the female Ornithorhynchus open 

 on a flat patch ; in Echidna, in a depressed area around 

 which a temporary pouch seems to be developed. There 

 are no distinct mammae. 



The vertebral centra have weak epiphyses in Orni- 

 thorhynchus^ and apparently none in Echidna. In the duck- 

 mole the post-sacral vertebrae are stronger than the pre- 

 sacral. The skull is smooth and polished as in Birds, for 

 the sutures disappear. The rami of the lower jaw do not 

 unite in front, have no ascending process, and have a slightly 

 inflected angle. In Ornithorhynchus there arc true mam- 

 malian teeth, but only in the young ; in Echidna none are 

 present. Cervical ribs remain distinct for a time at least ; 

 the odontoid process of the second vertebra is for a long 

 time free from the centrum. Except on the atlas of 

 Echidna, the cervical vertebrae are without zygapophyses 

 or articular processes. The (meta-) coracoids reach the 

 presternum ; there are also large epicoracoids and a 



sc., Scapula; <:/., clavicle; i.cl. 

 interclavicle ; cv., metacoracoid 

 c.co., epicoracoid ; sf., sternum. 



