1 40 Zoology of Colorado 



surface, but in the air. They had undoubtedly been introduced 

 with plants, and Mr. F. C. Baker, in his monograph of North 

 American Lymnaeidae, figured and described them as a species 

 unknown to him. Their place of origin, and proper specific 

 designation, still remain unknown. The habit of leaving the 

 water doubtless contributes to the spread of the liver fluke disease, 

 from which it was formerly estimated that a million sheep died 

 annually in the British Islands. A small snail, Lymnaea truncatula 

 (very closely related to one common in Colorado) harbors the 

 young liver fluke. The young flukes, leaving the bodies of the 

 snails, attach themselves to the grass at the edge of the pond. 

 This grass, being well grown and succulent, is eaten by the sheep, 

 and the flukes develop to full size in the livers of the unfortunate 

 animals, which consequently perish. The eggs of the flukes are 

 scattered over the pastures, and washed by rains into the ponds or 

 ditches, and so the snails become infested. 



The oldest known American Lymnaeas are three species de- 

 scribed by White, found in the Atlantosaurus Beds, of the Coman- 

 chean period, about eight miles north of Canon City. Two of 

 these, although many millions of years old, are very like species 

 still living. The third is peculiar, and perhaps belongs to another 

 genus. There are fossil species of Lymnaea, and also a Planorbis, 

 in the Miocene shales of Florissant. 



FRESHWATER BIVALVES OR CLAMS 



In Cretaceous and early Tertiary times the Rocky Mountain 

 region possessed a varied assemblage of large freshwater mussels, 

 such as may be found in the Mississippi Valley today. So far as 

 we may judge from the shells, they represented a number of ge- 

 nera now living, but the determination of genera in this group 

 from shells alone is a matter of great difficulty. In recent times 

 careful studies of the soft parts of living species have been made, 

 with surprising results, indicating a large number of diverse genera. 



Many years ago C. T. Simpson found five kinds of freshwater 

 mussels (Unionidae) in or near Lodgepole Creek, northeastern 

 Colorado, in the Platte drainage. Henderson notes that in the 

 report of the Fremont Expedition (1845) it is stated that in July 

 1842 Lodgepole Creek was a clear, handsome stream, with a 



