GEOGRAPHICAL DISTRIBUTION. 39 



to pulmonate life. In the number of its species, also, the Texas Region 

 is favored ; by adding to the above list of peculiar species those which 

 it has in common with all of the Eastern Province, and also those of 

 the Southern Region, we find a total of seventy species, the same num- 

 ber as found in Florida. 



On the accompanying map the Pacific Province is colored pink, the 

 Central Province blue ; the Eastern Province (of which the northern 

 portions are not shown) is uncolored. The subdivisions, or Regions, of 

 the Eastern Province are also indicated by colored lines. The red line 

 marks the division between the Northern and Interior Regions. From 

 this line the last-named region extends (its Sub-Region of the Cumber- 

 land shown by green lines) to the brown and yellow lines, which, taken 

 together, mark the northern boundary of the Southern Region, the yel- 

 low separately indicating the Texan Sub-Region, the brown the Floridan 

 Sub-Region. 



In the above pages I have simply stated the facts now known regard- 

 ing the actual distribution of our land shells, scarcely attempting to 

 explain it. I will here venture to make a few suggestions on this sub- 

 ject. 



The student of geographical distribution must now take as his guide 

 the recently published work by Wallace on this subject. 1 From this 

 he will learn that terrestrial mollusca of most of the recent genera have 

 existed on the globe from very early geological times. Also, that, 

 wherever originally appearing, their universal distribution over all the 

 continents is easily explained. Thus we readily account for their pres- 

 ence in North America, 2 and however imperfect may be the geological 

 record, it shows us that at least Zonites, Pupa, Helix, Bulimulus, Vi- 

 trina, Macrocyclis, and Clausilia existed here in previous geological 

 ages. From these ancestors, no doubt, have been derived, through many 

 intermediate stages of development, the present fauna. I have already 

 shown that the characteristic American genera of the Eastern Province, 



1 The Geographical Distribution of Animals, with a Study of the Relations of Living 

 and Extinct Faunas as elucidating the past Changes of the Earth's Surface. By Alfred 

 Russell Wallace. Amer. ed. Harper and Brothers. New York. 1876. 



2 In the following pages it will be seen that three well-established genera only — Hem- 

 phillia, Prophysaon, and Ariolimax — are peculiar to our limits, excepting perhaps a few 

 disintegrated Helix. 



