144 PHYSICAL GEOGRAPHY. 



MOLLUSKS.* 



Though not directly connected with the main question of this 

 chapter, yet, for convenience, the following brief enumeration of 

 our moluscan fauna is given. There being no sea-coast, only land 

 and fresh water forms are native to the State. Of these, the air- 

 breathers are well represented. The Vitrianas, a subfamily closely 

 allied to the snails, are represented by seventeen species. Of the 

 snails proper (Helicince), there are thirty species, the most abundant 

 of which is the Spotted Snail (Helix alternata]. There have been 

 classified of the Pupinae twelve species, of Succiniae eight species, 

 of Zonitinse seven species, these last being distantly allied to the 

 preceding group. The fresh water shells are even more abundant than 

 the preceding land shells. Thus far, there have been found of these 

 thirteen species of Limnaea, eight species of Physa, two of Bullimus, 

 twelve of Planorbis, one of Segmentina, four of Ancyclus, two of 

 Valvata, three of Vinipera, three of Melantho, two of Amnicola, 

 two of Pomatiopsis and five Melanians. These fresh water shells 

 having but one valve in a spiral are often .all popularly designated 

 as water snails. But the most abundant of all our fresh water 

 shells are the so-called clams (Unios and Anadontas]. Of the Unios 

 there are at least sixty-seven species, of the Margaritanas two, and 

 of the thin-shelled, muddy-bottom loving Anadontas there have 

 been fourteen species found in the State. These are the numbers 

 that I have identified, but as I have examined only comparatively 

 small sections of our rivers, it cannot be possible that all the species 

 came in my way. Many more species must, therefore, be added to 

 our list. In fact, I have often waded in our rivers for miles with- 

 out finding a single shell, and then, coming upon a hard or solid 

 bottom of limestone, the bed appeared lined with Unios of many 

 species. Before we know what our rivers contain of our molluscan 

 fauna, they must be closely examined along their whole length, a 

 task too severe for any one investigator. 



*For a specific list of our Land and Fresh Water Shells, the reader is referred to the 

 writer's Catalogue of the Land and Fresh Water Shells of Nebraska, published in Bulletin 

 3, Vol. III. of U. S. Geological Survey. 



