1896 NOTES AND COMMENTS. 79 



resembles a large Phascologale, or a small Dasynvus, while its dentition 

 is also like that of those species of Phascologale which approach 

 Dasyuvns. The skull, on the other hand, agrees with that of Smin- 

 thopsis in the character of the nasal bones, while the hindfoot in shape 

 and in the absence of a hallux differs from that of both Phascologale and 

 Sminthopsis. The specimens on which the description is based con- 

 sist of six males and one female, and the dimensions of an adult male 

 in alcohol are : — head and body, 182 mm. ; tail, 130 mm, ; ear, 18 mm.; 

 hindfoot, 38 mm. The new Sminthopsis is a small mouse-like form, 

 separated from the two known species, 5. murina and S. crassicaudata, 

 by a long, very stout, and highly incrassated tail, and by the greater 

 relative length of the hindfoot. 



A Placental Marsupial. 



The absence of a true allantoic placenta has for long been 

 regarded as a chief diagnostic character of the marsupials, distinguish- 

 ing them, as well as monotremes, birds, and reptiles, from higher 

 Mammalia. A recent discovery of J. P. Hill, demonstrator of biology 

 in the University of Sydney, , seems to destroy this generalisation. 

 As yet we have seen only a preliminary note [Pvocetdings of the Linnaean 

 Society of New South Wales, vol. x, p. 578), but the description and 

 figure seem to make it plain that in the short-nosed bandicoot, 

 Perameles obestda, an allantoic placenta occurs. The allantois is 

 well developed, large, and provided with an abundant blood-supply. 

 It consists of a long and somewhat flattened stalk and a terminal, 

 expanded, and much flattened vesicular portion. The mesoderm of 

 the outer surface of the allantois is fused with the mesoderm of the 

 serous membrane. The capillaries of the vesicular portion, containing 

 the foetal blood, become closely applied to the surface of the uterine 

 mucosa, and form with it a closely interlocking system, since they 

 dip down into the substance of the mucosa to form short villous 

 processes. The uterine mucosa is very richly supplied with blood, 

 the maternal capillaries forming a net-work on and near the surface 

 of the mucosa, so that the foetal and maternal blood are thus brought 

 into very close relation. The allantois of Perameles is thus functional 

 both as a respiratory organ and as an organ of nutrition. Although 

 this is truly an allantoic placenta, the differences between it and the 

 placenta of higher mammals are sufficiently plain. It is not necessary 

 to suppose that this marsupial placenta augurs a clear zoological 

 affinity between the Peramelidae and the Eutheria. But, no doubt, 

 Mr. Hill will discuss these problems when the complete account of 

 his investigations appears. 



The Plesiosauria. 



Mr. C. W. Andrews has been issuing useful additions to our 

 knowledge of the structure of the Plesiosauria, but in no instance 



