THE WEST-AMERICAN SCIENTIST. 



FRESH-WATER SHELLS. 



Over seventy-five species of 

 fresh-water molluscs have been 

 described from the Pacific slope; 

 but of this number many have 

 been, and probably many others 

 must bft consigned to synonymy, 

 thus reducing the real number to 

 not more than fifty valid species. 



Of the common species belong- 

 ing to the family of Limnceidce, 

 inhabiting the small streams and 

 lagoons o£ Southern California, 

 but one can "be said to be charac- 

 teristic, the others having a dis- 

 tribution throughout the northern 

 United States. Our species of 

 Limmeidae are as follows: 



Limnsea humilis, Say. 



Limnsea Adelinse, Try on, (Cali- 

 f ornian. ) 



Physa heterostropha, Say. 



Physa distinguencla, Tryon, (=P. 

 gyrina, Say. var.) 



Planorbis parvus, Say. 



Planorbis trivolvis. Say. 



It will be seen that in fresh- 

 water, air-breathing molluscs we 

 have no typical fauna. This shows 

 that they are not materially af- 

 fected by the climate or other 

 physical conditions surrounding 

 them; but while these conditions 

 which so widely separate the 

 north-eastern from the south-west- 

 ern portion of the United States 

 are immaterial to these little crea- 

 tures, they are all sufficient to cre- 

 ate an almost wholly different fau- 

 na and flora, otherwise. 



Bithynella intermedia, Tryon, 

 and BithyneJla binneyi, Tryon, 

 with Pisidium abditum, Hald. 

 (our only bivalve) complete the 

 list of the fresh-water shells of 

 San Diego county, excepting the 



living and extinct species of the 

 Colorado river and the desert 

 basin. 



BLACK WATTLES. 



This tree (Mimosa decurrens) 

 a native of Australia, has been 

 introduced into the south of 

 France, Algiers, etc., and is highly 

 recommended by European nur- 

 serymen as a tree "careless of 

 drouth, doing its best on dry, bar- 

 ren soil, of rapid growth, and very 

 rich in tannin." 



This is perhaps, one of the most 

 promising of trees for forest plant- 

 ing in Southern California and de- 

 serves a thorough trial. Plants 

 grown from seed have kept equal 

 pace with seed started at the same 

 time of the blue gum Eucalyptus, 

 which is now the leading forest 

 tree of the state in cultivation. 



AIR NAVIGATION. 



[Science.] 



Renard and Krelbs, of France, 

 by the use of a powerful and light 

 motor and a long balloon, have 

 reached a speed of 6.5 metres a 

 second in their recent experiments 

 of November, 1884, in aerial navi- 

 gation. During these experiments 

 the balloon was easily guided in 

 all directions and a return to the 

 place of departure easily effected. 

 These experiments are decisive in 

 demonstrating navigation of the 

 air by means of long balloons, pro- 

 vided with screws, and it now be- 

 comes only a question of capital 

 for aerial ships to take their place 

 among the modern means of trans- 

 portation. 



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Exchange notices inserted at five cents 

 per line. Stamps taken. 



