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MR. A. MURRAY'S MONOGRAPH OF THE FAMILY OF NITIDULARLA. 229 
its descendants had under the new conditions changed into Sf. didyma and given off 
cousins now called St. orphana, and that all this had been done within the short space 
of a couple of centuries, probably much less. A similar explanation would do for the 
Tahiti species, with this difference, that its parent was probably Stelidota ruderata from 
the West Indies. The variations in these are slight, and very different in degree from 
the class of phenomena of which the existence of the new genus Lordyra, found by 
Mr. Wallace in Celebes, is an example. 
There are other genera which, although almost entirely confined to one country, are 
also represented in some other distant lands by one or two exceptional species. "There 
is the genus Lobiopa, of which there is one species in North America, several in Mexico 
and the West Indies, a greater number in Brazil, Para, and Columbia, two species in 
Peru, and one in Senegal. The Peruvian species are obviously outliers from Columbia. 
The district about Quito embraces many species of plants and animals which are called 
Peruvian or Columbian according as they are most frequent in Peru or Columbia; and 
when we see the same species thus found on both sides of the Andes, it is natural to 
expect that different species of the same genus should also be found. But it is different 
with the Senegal species. I have already, in a paper published in this Society's * Trans- 
actions,’ * On the geographical relations of the Coleoptera of Old Calabar," pointed out 
the occurrence on that part of the west coast of Africa of species belonging to genera 
of remarkable facies which had up to that time been supposed to be peculiar to the 
opposite coast of South America, and in that paper I briefly discussed the question 
whether their presence on the west coast of Africa, and similar instances of the converse 
where West-African forms are met with in Brazil, could be referred to the proximity or ` 
junction of the two continents at some former period of time not so distant as to have 
allowed great changes in the fauna to be gradually effected. The Nitidularie furnish a 
number of instances illustrative of this point. Besides Lobiopa, the Brazilian genus 
Platychora has representatives in Africa; there are species of Perilopa both in Africa and 
Brazil; and Old Calabar furnishes at least two species of the American genus Prome- 
topia—although this is of less importance, as other species are found in the East Indies 
and Philippine Isles. 
An interesting point in the distribution of genera which are thus widely spread is the 
fact that they are not found in numbers in these outlying districts: the number in what 
we may call the metropolis of the genus may be considerable; but we find that of those 
located elsewhere very limited—one dropped here, and another there, at immense dis- 
tances. Take Prometopia: we find one species of it in North America, one in Mexico, 
four in Para, &c., two in West Africa, one in the East Indies, and six in the Malayan 
Archipelago. Others, again, seem equally scarce everywhere. We know of one species of 
ZEthina in Madagascar, one in the East Indies, one in Australia, one in Africa, and one 
in Mexico. With the exception of the genera Colastus and Camptodes, peculiar to Ame- 
rica, I do not remember any genus containing numerous species which is confined to 
one hemisphere. Of course where a genus has only one species it must be confined to 
one hemisphere, unless indeed the species is cosmopolitan (and I know of no instance 
where a genus with only one species has that species widely distributed). 
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