949 



and its northern limit ranges in both hemispheres with the parallels 

 of equal temperature laid down by Humboldt. The calcified condi- 

 tion of the genus corresponds also with the curves northward in the 

 isothermal lines along the west coast of South America and those 

 bending southward on the east side ; the Bulimi having a colder 

 aspect in Chili from the cold precipitated by the great Antarctic 

 current of cold water which flows nearly to the Gallapagos Islands, 

 than those of the opposite Brazilian coast which are affected by the 

 equatorial current. In Patagonia the genus is suddenly arrested in 

 a tropical condition by the recent geological changes that have taken 

 place in that now barren and riverless country. The memoir pro- 

 ceeds to show that in the distant islands ol' the Pacific the Bulimi 

 are curiously represented by other genera of terrestrial moUusks; 

 whilst the species of islands approximating to continents, such as 

 Trinidad, partake of the character of tliose of the main land. 



The European species belong to the Caucasian type, wliicli has its 

 centre in Asia Minor, where the shell is mostly colourless, owing to 

 the dry, juiceless, thorny character of the vegetation which affords 

 little nutriment, and the Bulimi live mostly under blocks of wood or 

 stone. This type reaches nearly to the south-eastern corner of Asia, 

 where it is suddenly met at Birmah and in the Malacca peninsula 

 by the richly-coloured Malayan type, which is so abundantly and 

 beautifully represented in the islands of the Eastern Archipelago. 

 The distribution of the genus among these islands is remarkably 

 local. The Bulimi of North Africa partake of the character of those 

 of Europe, whilst those inhabiting south of the equator belong to a 

 totally different type. 



The precise localities and circumstances of habitation of the 

 various genera of Mollusca have as yet been too imperfectly noted 

 by travellers to aid much in determining the laws relating to geogra- 

 phical distribution. The present summary of collected facts may 

 prove suggestive of more careful observation, and, in the hands of 

 those who are acquainted with the geological and physical history of 

 the earth's surface, lead to important and interesting results. 



The paper is illustrated with a map constructed with tints of 

 shade, colours, and isothermal lines. 



2. " On the influence of Physical Agents on the development of 

 the Tadpole of the Triton and the Frog." By John Higginbottom, 

 Esq. Communicated by Thomas Bell, Esq., Sec. U.S. 



Mr. Higginbottom's experiments were made in different positions 

 and degrees of temperature, many of them in a rock cellar 30 feet 

 deep, where no solar light ever entered, and where the temperature 

 varied only in the course of the year from 48° to 55° Fahr. 



The results of numerous experiments showed that the development 

 of the tadpole was principally hastened or retarded by temperature 

 and the supply of food, and that, contrary to the opinion of many 

 other observers, the presence or absence of light did not appear to 

 exercise any perceptible influence upon their development. 



