MOLLUSCA 141 



uniform breadth of 22 feet, and six inches in depth. Simpson 

 states that in his time (the '80s of the last century) it was six to 

 eight feet wide, and sometimes went dry. In 1912 Professor 

 Henderson and Dr. M. M. Ellis visited the spot and found the 

 stream narrow and shallow with only one pool on the Colorado 

 side of the boundary. Nothing could then be found of Simpson's 

 mussels, except a few dead shells of one species (Anodontoides 

 ferussacianus). Although our mussel-fauna in the northeastern 

 corner of the State has thus apparently perished, certain species 

 exist elsewhere, and it is probable that irrigation operations have 

 even favored the spread of one or two kinds. At all events, 

 Strophitus edentulus race pavonius of Lea has been obtained at 

 Windsor and east of Boulder, while Anodonta grandis of Say is 

 reported by Henderson 30 miles north of Denver. Other species 

 have been found in Black Wolf Creek, Yuma County, and Carrizo 

 Creek, Las Animas County. Careful search should be made in 

 all counties along the eastern border, and it may be that additional 

 forms will be discovered. 



The small freshwater bivalves are placed in the genera 

 Sphaerium, Musculium and Pisidium. The first two include 

 shells of moderate size, but considerably less than an inch in 

 diameter, more or less transversely oval, and considerably swollen. 

 A member of this group {Sphaerium or Musculium florissantense) 

 is found in quantity fossil at Florissant. Among the modern 

 species, the most interesting is the handsome Sphaerium hender- 

 soni of Sterki, discovered by Henderson in Crow Creek, northeast 

 of Greeley, and described in 1906. Henderson revisited the 

 locality in 1912 and 1921, but the little clams could not be seen, 

 and no one knows at present where they may be found alive. 



The genus Pisidium (the name meaning like a pea) consists 

 of much smaller shells, the Colorado members looking like small 

 pebbles if not closely examined. They abound in our mountain 

 lakes; numerous species have been found, several of them new to 

 science. Henderson gives a table of localities, twenty of them 

 10,000 feet altitude or over. Two or three species were found 

 in a lake north of Corona, at an altitude of 1 1,500 feet. In 1887 

 I found a small and peculiar species in Surface Creek, on the 

 north side of the Grand Mesa, at 8,500 feet. Unfortunately it 

 has never been collected since, and its characters are little known. 



