1Y4 AMERICAN JOURNAL 



tates Conchologicse," botli of which are mainly devoted to the 

 description of terrestrial species. 



The following list of Dr. Pfeiffer's works will show at once 

 the extent of his labors, and the rapid progress of this branch 

 of the science : — 



Symholse ad Historiam Heliceorwn. I., 1841, II., 1842. III., 

 1846. 



Contains Tables of Synonymy, with descriptions of ninv or 

 imperfectly known species only. In the third part, the spe- 

 cies of Helix are arranged on the plan which the author has 

 since used for all the genera. 



Monographia Heliceorum viventium. I., II., 1848. 1075 pp. 



2278 species. 

 III., 1853. 711pp. 3882 



species. 

 IV., 1855. 920 pp. 5159 

 species. 

 Monog. Aitriculaceorum viventium. Y ., 1852. 209 pp. 242 sp. 

 " Pneumonopomorum " I., 1852. 439 pp. 735 sp. 



II., 1858. 249 pp. 899 sp. 

 " III., 1865. 284 pp. 1686 sp. 



The very large increase in the number of operculated shells 

 is owing, in a considerable degree, to the researches of natural- 

 ists and travellers in Cuba. The increase of species of oper- 

 culate terrestrial shells in the principal genera, may be desig- 

 nated thus: — 



