98 THE NAUTILUS. 



should be removed from Nodularia and be placed in Unio next to the 

 Unionid section Lapidosus. Still the situation requires heroic treat- 

 ment. One or two obvious points are: 



(1) Nodularia orientalis Lea is placed by Mr. Simpson in this 

 genus, it is true, as he observes, with much doubt because of paucity 

 of material. This shell, however, both by its geographical distribu- 

 tion as well as by its whole facies, belongs to the genus Rectidens. 



(2) Nodularia pazii Lea. This shell and ingallsiana Lea have 

 sandwiched between them the Nodularia jourdyi. Yet these species 

 are by no means akin, the latter being a true Nodularia, while for 

 the accommodation of the other two species, and probably others, a 

 new genus should be erected. 



The Unio ingallsiana Lea differs generically from Nodularia in 

 having little or no beak sculpturing and in having a smooth shell. 

 Its cardinal teeth are blade-like and double in the right valve 

 and single in the left. The cardinal teeth form a part of the 

 general inner curvature of the shell, not having a " fulcrum " (as the 

 buttress-like thickening of the noose supporting the cardinal teeth, 

 and extending posterior to the adductor scar, may be called), which 

 is so generally shown in most Unionidce. Tlie '• third anterior 

 muscular scar " is separate from the anterior adductor scar, whereas 

 in Nodularia they are always confluent and not easy to differentiate. 



For those shells, as the Unio pazii Lea (and ingallsiana Lea), 

 exhibiting these characters as outlined, the writer proposes the new 

 genus Ensidens. Two other peculiarities "of the two species named 

 may prove to be of generic significance, but at present they may be 

 regarded as being of specific import merely. These are the entire 

 confluence of the anterior adductor and the " protractor pedis" mus- 

 cle scar, and that the escutcheon is half way the length of the lateral 

 teeth. 



CIVILIZATION AND SNAILS. 



BY V. STERKI. 



It is known that in a general way land and fresh-water mollusks 

 have been decreasing in numbers in consequence of deforestation 

 and cultivation of the land, directly and indirectly by the atmos- 

 phere becoming more dry, the disappearance of springs, drying up of 



