8 Transactions. — Zoology. 



have the metatarsus more robust and its trochleas more ex- 

 panded than those from Glenmark. The representatives of 

 Mesopteryx casuarina at Enfield have the tibia about 17*5in. 

 long, while in those from Hamilton it averages 18'25in. These 

 instances are sufficient to show that the species are not more 

 restricted than is necessary for convenience of description. If 

 they were made larger we must either use a cumbersome 

 system of sub-varieties ; or else, by clubbing varieties to- 

 gether, lose all chance of solving our problems. No one, I 

 presume, at the present day would refuse to recognise two 

 species because intermediate links had been found. This is a 

 pre-Darwinian idea, which means that before a group of indi- 

 viduals may be allowed to form a distinct species all the steps 

 of the ladder on which it rose must be destroyed. This would 

 be a very hard rule for the palaeontologist to obey, for he would 

 have to examine and classify the mutations by which one 

 species changed into another without being allowed to give 

 distinct names to any of them. 



The difficulties involved in making a correct classification 

 of the moas are due partly to the gradation of characters 

 during the long interval between the earliest and latest forms 

 known : partly to their extraordinary number, through which 

 bones belonging to some three or four genera and ten or 

 twelve species are usually found mixed together : and partly 

 to collectors who either do not preserve intact individual 

 skeletons or, what is much worse, add a bone or two to make 

 a skeleton more complete. These difficulties are so great that 

 the task of straightening things out appears almost hopeless. 

 Nevertheless they must be faced if the problems I have men- 

 tioned are to be solved ; and we can only hope that by con- 

 stantly correcting our mistakes they may in time gradually 

 disappear, and we shall then be able to write the remarkable 

 history of the development of the moas in New Zealand in 

 considerable detail, and with considerable confidence that we 

 are giving a fairly-true representation of what really took place. 



Descriptions of New Species. 

 Dinornis strenuus. 



This species contains all the birds from the South 

 Island which have, up to now, been included in D. struthi- 

 oides. I formerly thought that the differences between the 

 birds of the two Islands were not sufficient to separate them ; 

 but I find that those from the South Island have constantly 

 the metatarsus more robust, and with more widely diverging 

 trochleas than those from the North Island. In D. strenuus 

 also the tibia is rather shorter and more robust than in D. 

 struthioides. These differences — which will be seen in the 

 following table — when combined with a difference in geo- 



