464 NATURAL HISTORY OF BIRDS. 



Passeres, and, as the present super-family contains a great many different forms of 

 tarsal scutellation, we may improve the opportunity by familiarizing ourselves with 

 a few of the modern technical terms, which in one word express quite marked 

 differences. 



The first distinction to be made is between a scutelliplantar and a laminiplantar 

 tarsus. In the former, at least one of the sides of the posterior tarsal surface is 

 divided by transverse sutures or is broken up into small scutellas. The laminiplantar 

 tarsus is covered behind with a continuous horny lamina on each side, without sutures 

 or divisions. This arrangement is found in all true Oscines (Passeroideae) with the 

 exception of the larks, and is only met with in a few Old World forms of the present 

 super-family, viz., in the Pittidas, which also have the tarsal covering in front undi- 

 vided, or ' booted ' (ochreatce). 



The scutelliplantar tarsus shows several modifications. The anterior scutes may 

 extend round to the posterior margin extei'iorly, leaving the internal plantar space 

 covered by a smooth skin, with no signs of scutes or scutellaa ; such a tarsus is said to 

 be exaspidean. Or the arrangement may be reversed, so that the anterior scutes are 

 extended round the tarsus on the inner sides, in which case it is endaspidean. If the 

 posterior surface of the tarsus is entirely broken up into numerous small, somewhat 

 irregular and rounded scutellaB, the tarsus is pycnaspidean, while taxaspidean means 

 that the plantar scutelhe are contiguous, rectangular, and arranged in regular series. 

 If, as in the larks, the scutellation behind is formed by larger scutes in a single series, 

 the term holaspidean has been used. In the taxaspidean tarsus it often occurs that 

 all the scutellaa become fused in the old birds, which then have a booted tarsus, and 

 such may be the origin of the nature ,of the tarsus of the Pittidas, while the true 

 ochreate tarsus, as it is found in the thrushes, is formed by simple fusion of the ante- 

 rior scutes only. 



In this connection it may be well to remember that only the Passeroideaa, or the 

 acromyodian Passeres, are laminiplantar or holaspidean, and that most mesomyodian 

 Passeres have ten primaries, the first of which is but slightly shorter than the rest. 



The Tyrannoideas are found in both hemispheres, though not one tenth of the 

 nearly six hundred species composing the super-family inhabit parts of the Old 

 World. They are chiefly tropical, and it is only in America that birds of this group 

 extend their range considerably beyond the limits of the tropics, though the number 

 of species Avith such a distribution is comparatively small. Of the Old World forms, 

 one family inhabits parts of the Australian, Oriental, and Ethiopian regions, while an- 

 other is restricted to Madagascar, and a third to New Zealand, a distribution of allied 

 birds which, after what we have seen on preceding pages, cannot be strange to the 

 readers of this volume. 



A considerable diversity of form is shown by the members of this super-family. 

 We have already mentioned the different tarsal structure to be found amongst them, 

 but the bills and general habitus is also very variable. We will soon be introduced 

 to forms which resemble the starlings, with their loncj and straight bills ; others seem 



' r \J O / 



to have copied the thrushes, while again others have all the superficial look of a 

 wren, and true flycatchers and shrikes are closely mimicked by tyrant-flycatchers and 

 the ' American bush-shrikes ' ; even the ' conirostres,' finches, or tanagers, are not 

 unrepresented in the clamatorial Mesomyodi. Indeed, so great is the external 

 resemblance of these with some form or another of true Oscines that before their 

 internal structure had become known they were classed with the isomorphic oscinine 



