1896.] ON MAMMALIAN DENTITION. 557 ' 



Nitzsch in Trachyjphonus and Pkus and it also exists in lynx and 

 lihamphastos. 



A further likeness between the three families of birds concerned 

 is in the surrounding of the oil-gland by the spinal tract. This 

 occurs, as wiU be seen from Nitzsch's figures, in both Picus and 

 Bhamphastos. 



If Nitzsch's figures of Capita {Micropogon) cayennensis are 

 correct, we may have in the pterylosis a means of differentiating 

 the Old World from the New World Barbeta. For in the latter 

 the posterior part of the spinal tract is separated from the anterior 

 and is composed of two distinct limbs which only join just at the 

 oil-gland. I would further point out that the identity in the 

 pterylosis of Megalcema and Cyanops is against their generic separ- 

 ation. On the other hand, the pterylosis of Xantholcema rosea is 

 very different from that of Megalmma, which justifies its retention 

 as a genus. 



There is the usual interscapular fork, but there is no break, a 

 rhomboidal apterion being enclosed, as is so far correctly shown in 

 Nitzsch's figure ; but although the two halves of the spinal tract 

 do join, the junction is produced only by their lying close side by 

 side and they immediately diverge to end at the sides of the oil- 

 gland. The tract, in fact, has an hourglass-like shape, which is 

 merely an exaggeration of that which, according to Nitzsch's figure, 

 characterizes the Toucans. 



In the lateral and femoral tracts Xanilwlmma agrees with Mega- 

 Icema. I find, after examining Selenidera macuUrosiris and Aulaeo- 

 rhnmphiis prasinus, that all the Toucans do not agree with Nitzsch's 

 figures of lihamphastos erythrorhynchus. In the two just-men- 

 tioned birds there is no break in the spinal tracts, which are thus 

 more like those of Xantholcema. The femoral tracts do not arise 

 from the spinal tracts so high up as is figured by Nitzsch, and the 

 lateral tract, apparently absent altogether from Aulacorhamphus, is 

 very rudimentary in Selenidera, consisting of only three or four 

 feathers. 



3. Contributions to the Study of Mammalian Dentition. — 

 Part II.' On the Teeth of certain Insectivora. By M. 

 F. Woodward, Demonstrator of Zoology, Royal College 

 of Science, London. 



[ReceiTed May 5, 1896.] 

 (Plates XXIII.-XXVI.) 



In their general organization the Insectivora are undoubtedly 

 very primitive, consequently one might reasonably expect to find 

 their dentition in a similar lowly state. This at first sight appears 

 to be the case, at least so far as the pattern of the molar teeth is 

 concerned, for if we accept the tritubercular form as the primitive 

 1 For Part I., see P. Z. S. 1893, p. 450. 



