169 



Moth ; a South-Eastern European element represented by 

 the Tiger Beetle, and the Clausilia amongst the Mollusca ; 

 and a central European element in the beautiful Thorn 



.Moths.* 



Although this theory undoubtedly accounts for the distri- 

 bution of many species of animals, it by no means accounts 

 for all. Species may have arisen in centres that are now 

 lost, because the species there have died out ; and where a 

 genus is now most highly developed, this has not always been 

 the case, as palaeontology shows. For instance, in the first 

 section of this paper we saw that the genus Astarte, though 

 now so abundant in northern seas, was in Jurassic ages 

 most numerous in the warm seas of Central Europe. 



Where fossil evidence is lacking, as in the majority of 

 insects, speculations as to their original homes must at the 

 best be hazardous. One of the beetles mentioned as living in 

 Greenland belongs to the genus Creopliilus, which attains its 

 maximum development in New Zealand where there are six 

 species, a seventh occurs in South America, and the eighth, C. 

 ntaxillosus, is the European form. According to the theory 

 of centres of distribution New Zealand should be regarded 

 as the place of origin of these insects, hut it is quite clear that 

 the species of this group originated at a time when the present 

 distribution of land and water was quite different, and that 

 the home of the genus may have been in lands now beneath 

 the sea. That the species of a genus originated in a centre 

 cannot be disputed, but it would be erroneous to suppose 

 the present distribution of the species indicates this centre. 



VI.— CONCLUSION. 



Having reached the end cf our survey of the zoology of 

 Cleveland, past and present, it only remains to sum up 

 the chief conclusions we have drawn from it, and to take a 

 comprehensive view of the evolution of the fauna as a whole. 

 We saw that the earliest fauna of the district is a marine one, 

 and dates back to the late Triassic Period. This fauna was 

 in its turn succeeded by the numerous faunas of the Lias and 



*For further details see Scharff's " European Animals, their Geological 

 History, etc," and "History of European Fauna." 



