PART II. 



UNIONID^E. UNIONIN^E. 



377 



very short, the posterior gaping; cardinal teeth f 

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

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



TRIBE 3. ATRACHIA. 



Animal without siphons. 



FAMILY 1. UNIONISE. River Muscles, or Unto*. 



Animal fluviatile ; shell solid, perlaceous j generally with 

 cardinal and lateral teeth. 



SUB-FAM. 1. UNIONINJE. 



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

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

 longitudinally undulated. 



UNIO Lam. Cardinal teeth short, oblique, receding from 

 the anterior margin of the shell, (fig. 123. h.) 



Unio. Oval or round, but never winged ; bosses very 

 prominent ; 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. 



