22 Trans. Acad. Sci. of St. Louis. 



Unio ligamentinus Lamarck. 



Plate XXL 

 Animaux sans Vertebres, Ed. 1838, Vol. YI, p. 533. 

 Described as follows: — 



U. testa ovali tumida, sub epiderme Candida; ligamento 

 subdupUci : unico externo detecto ; allero intra natem et car- 

 dinem obtecto. 



^' Habit e la riviere de r Ohio. A. Micltaud. La coquille 

 a sur chaque valve un angle obtus au cote anterieur. Son test 

 est tres blanc. Son corselet est un peu eleve en carene. Dent 

 cardinale fort epaisse. Largeur, 77 millimetres.'" 



It is quite possible that the very extensive synonymy 

 that is exhibited by this species is due largely to the 

 incomplete description which Lamarck gave to this form. 

 It is widely distributed over the United States from western 

 New York to Michigan, Minnesota, Dakota, and Kansas ; 

 south to Texas, Louisiana, Alabama, and Tennessee. In 

 this vast range, throughout which it is common or abun- 

 dant, it has a wonderfully diversified environment. Its home 

 may be in sluggish and muddy bayous, where it delights to 

 dwell in mud and sand ; in rapidly flowing mountain streams, 

 like the upper Cumberland and the Holston rivers, where it 

 may be found on gravel bars or wedged in between the larger 

 rocks in the middle of the channels ; in the muddy or gravelly 

 rivers of the western prairie States, as in Iowa and Illinois, 

 where it dwells indifferently in mud or gravel. It follows 

 therefore, that these great differences in environment will be 

 influential in determining its coloration and its form. So it is 

 among the most variable, in minor details, of any of the com- 

 mon river-mussels of the western States, sharing in this regard 

 the changes in form incident to Unio luteolus Lamarck and 

 Unio complanatus Solander, the last named being a form which 

 has never yet been found in any stream west of the Appalach- 

 ians, outside the drainage of the Great Lakes. These very vari- 

 able shells have been described many times by those who look 

 for differences rather than resemblances, and so the great 

 burden of synonymy has arisen. A partial list of the most 



