OF CONCIIOLOQY. 229 



2. Southern Atlantic States — South Carolina to Florida. 



2, S. inflata, 4, S. campeslris, 6, S. effusa, 26, S. Wilsonii, 



29, S. luteola. 



3. South-western States — Mississippi, Louisiana and Texas. 



3, S. unicolor, 8, S. Greerii, 9, S. Grosvenorii, 27, S. For- 



ahey'i, 28, $. concordialis, 31, S. Salleana, 33, S. Hale- 

 ana, 



4. Pacific States — California, Oregon, British Columbia, 



Nebraska, etc. 

 5, S. Stretchiana, 13, S. Gabbii, 15, S. lineata, 16, S. 

 Mooresiana, 17, S. Oregonensis, 18, $. rusticana, 19, 

 $ Haydeni, 20, & Sillimani, 25, A Nuttalliana, 30, 

 #. Hawhinsii. 



We thus find that our as yet imperfectly-known fauna ex- 

 hibits thirty-three well characterized species of Succinea, and 

 exceeds greatly those inhabiting Europe, which, in the last 

 edition of Pfeiffer's Monograph, number thirteen.* 



This extraordinary development of species of a single genus 

 of terrestrial Mollusks upon our Continent is the more remark- 

 able from the fact that in other terrestrial genera common to 

 the two Continents, our fauna is by no means so rich as that of 

 Europe. In Helix, Bulimus and Pupa, the species are not 

 nearly so numerous with us. 



Several species of Succinea inhabit Mexico, Central America 

 and the West India Islands, but their number is not so great 

 as would be expected from the considerable quantity of other 

 types of terrestrial Mollusks in those countries. In fact, the 

 paucity of these forms leads to the conclusion that the maxi- 

 mum development of these groups [Succinea and Brachyspira) 

 of the genus is within the limits of the United States, and that 

 the principal species are inhabitants of the temperate zone of 

 America and Europe. 



* It is remarkable that Pfeiffer and Albers (Heliceen, 1861} have both 

 failed to recognize the true characters of the two groups of Succinea in- 

 habiting Europe. Although their definition of Brachyspira is sufficiently 

 correct, yet they have so distributed the species as to show that they re- 

 garded these divisions as very arbitrary, not as natural ones. Thus, we 

 have almost every species of Brachyspira, European and American, placed 

 by these authors in their sub-genus or group Succinea, whereas almost 

 every European species is a true Brachyspira. We may instance S. Pfeif- 

 feri, S. longiscata, S. Italica, etc. S. Uumilis, S. Baudoni, etc., may be 

 classed as typical Succinece. 



