OBSERTATIONS. 



The shell which we have designated by the above name 

 is closely related to triqueter Raf. ; but differs in the greater 

 prominence of the superior portion of the anterior margin ; 

 the shorter posterior margin and lunule ; the direct car- 

 dinal teeth, and the little obliquity of the lateral ones. It 

 was sent to me from Nashville by Dr. Troost. I may re- 

 mark that some of the shells of Cumberland river vary 

 much from their corresponding species of other streams, 

 if I may judge by several specimens which I have seen 

 from that river. 



In stating the generic character, the number of muscu- 

 Jar impressions is said to be two, by which is understood, 

 two principal ones, for that there are many smaller ones 

 is familiar to all those who have examined these shells. 

 Dr. J. G. Klees in his" Dissertatio Inauguralis" (for which 

 work I am indebted to Dr. L. D. Schweinitz) says " mus- 

 culis duobus binis majoribus clausoribus accessoriis." Fe- 

 russac in his "Notice sur les Etheries" says "Presque 

 toutes les mulettes et les Anodontes offrent quartre im- 

 pressions separees, et Ton n'a point encore distingue d'une 

 maniere comparative celui des muscles d'attache que dans 

 leur position variee acquiert une predominance sur les 

 autres, selon la forme de I'animale la grosseur ou la figure 

 des valves." The four principal cicatrices of course exist 

 in all the species of this family, but they are sometimes so 

 approximated in pairs as to form but two or three separate 

 impressions. The several smaller cicatrices in the cavity 

 of the beaks indicate points of the attachment of small 

 dorsal muscles, for the secure support of that part of the 



PI. 51. 



