PART II. 



UNIONID^. UNIONIW^. 



377 



very short, the posterior gaping ; cardinal teeth ^ 

 or -I, small and nearly parallel ; ligament external. 

 V. irus. Poll, i. pi. 10. f. 1,2. ; and ii. pi. 19. f. 25, 26. . 



Tribe 3. ATRACHIA. 

 Animal without siphons. 



Family 1. UNIONID^^. River Muscles, or Uriios. 



Animal fluviatile ; shell solid, perlaceous ; generally with 

 cardinal and lateral teeth. 



I * 

 / 



SuB-FAM. 1. UNTONIN.E. 



One valve, with two cardinal and tw^o lateral teeth ; car- 

 dinal teeth short ; the mnbones, or bosses, smooth or 

 longitudinally undulated. 



Unio Lam. Cardinal teeth short, oblique, receding from 

 the anterior margin of the shell, {^jig, 123. //.) 



JJnio. Oval or round, but never wdnged _; bosses very 

 prominent j cardinal teeth very thick. 



U. Mytiloides Rafinesque. sulcata. Lea. Am. Tr. iii. 

 circula. Lea. Am. Tr. pi. 8. f. 12. 



iii. pi. 9. 14. cornuta Barnes. 

 torsa Rafinesque. 



