220 



Buenos Ayres, extending in the widely-distributed B. sporadic/is to the 

 banks of the Rio Negro, but none are recorded from the sterile, riverless 

 plains of Patagonia. That the genus should be suddenly arrested at this 

 point in a tropical condition, without any of the graduated forms which 

 abound in the north temperate countries of both hemispheres, is doubtless 

 owing to the upraising of the land in this part of South America, which 

 Mr. Darwin considers to have occurred within the period of the now-exist- 

 ing sea-shells. Mr. Cuming collected worn shells of Valuta Brasiliana (a 

 species living on the shores of Buenos Ayres) in a bank of other dead 

 sea-shells fifty miles inland. The climate is many degrees warmer in Pata- 

 gonia and Tierra del Puego than in the same latitude of the northern hemi- 

 sphere. " Evergreen trees," says Mr. Darwin, f< flourish luxuriantly under 

 it, humming-birds may be seen sucking the flowers, and parrots feeding on 

 the seeds." Snails being of less fugitive character than birds, and having 

 fewer means of transport than plants, appear not to have migrated thither. 

 The sea which washes the shores of Patagonia is peopled with a fauna of 

 more tropical character than the land, owing to the warmth of the great 

 equatorial current, which flows southward along the eastern coast of South 

 America, and causes a bend in the system of isothermal lines laid down by 

 Humboldt of nearly ten degrees. A fine large richly painted Volute, V. 

 Magellanica, in common use among the Patagonians as a. drinking-cup, 

 inhabits their shore abundantly. Yet the northern limit of this genus 

 does not approach the Mediterranean nor any part of Europe. It is right 

 however to add, that a species of Cymba, to which genus V. Mag elidible a 

 is the nearest allied form of Volute, has been very recently dredged off 

 Lisbon by Mr. M'Andrew. 



3. The Chilian Province. 



Crossing to the west side of the American continent and returning 

 northward, we are impressed with the marked difference between the 

 Bull ml on the west and those on the east side of the chain of the Andes. 

 In the sandy plains of Chili, where there is little moisture beyond that 

 arising from the dews, the Bullmi, about thirty-five in number, are mostly 

 small, with thin, often transparent shells, having little of colour or mark- 

 ing. Towards the mountains at the roots of shrubs, on dead trunks of 

 trees or under Cacti, are several species distributed somewhat miscellane- 

 ously in respect of form, as B. granulosus, ergthrostoma, Piriformis, etc., 

 Near the sea-shore they assume a more distinct typical character, of which 

 the shell, Succiuea-like, is widely inflated, and owing to the dry calcareous 

 nature of the soil and absence of vegetation is extremely thin, brittle, and 

 simply dark-speckled. The B. Broclerijni, punctullfer, rupicolus, and 

 refiexus are characteristic examples. Surrounded with few of the condi- 

 tions which serve for the formation of shell, the calcifying functions of 



