206 



angle witli the b'ase, obtusely emarginate in the middle by the 

 termination of the groove; umbonial slope carinated, in conse- 

 <|uence of the depression of the anterior side ; lunule very short ; 

 posterior margin very short, rounded ; color light brownish, obso- 

 letely radiated ; within white ; cardinal teeth direct ; lateral teeth 

 rectilinear, short, with but little obliquity ; posterior accessory ci- 

 catrix obliquely elongated, slender; anterior accessory cicatrix 

 confluent. 



Unio nexus, nob. Transylvania Journal, vol. 4, p. 527, 1831. 



Unio arcxformis. Trans. Amer. Philos. Soc, vol. 4,iV". S. 1832. 



The shell which we have designated by the above name is 

 closely related to triqueter, Raf., but differs in the greater promi- 

 nence of the superior portion of the anterior margin, the shorter 

 posterior margin and lunule, the direct cardinal teeth, and the little 

 obliquity of the lateral ones. It was sent to me from Nashville 

 by Dr. Troost. I may remark that some of the shells of Cumber- 

 land 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 muscular im- 

 pressions 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 " Disser- 

 tio Inauguralis," (for which work I am indebted to Dr. L. D. 

 Schweinitz,) says, " musculis duobus binis majoribus clausoribus 

 accessoriis." Ferussac, in his '' Notice sur les Eth6ries," says, 

 " Presque toutes les muUttes et les Anodontes offrent quartre im- 

 pressions separ(?es, et Ton n'a point encore distingue d'une mani^'-re 

 comparative celui des muscles d'attache que dans leur position 

 varie acquiert une predominance sur les autres, selon la forme 

 de I'animale, la grosseur, ou la figure des valves." The four prin-, 

 cipal 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 dor- 

 sal muscles, for the secure support of that part of the animal. The 

 palleal impression is also very distinct. These dorsal cicatrices, 

 were, no doubt, taken into acccount by Mery, Mem. Acad. Royale 

 des Sci. for 1710, p. 409, who says that there are eight muscles 

 attached to the inner surface of the shell. PI. 51. 



