128 THE NAUTILUS. 



Smooth, olive green; sometimes radiate with pale yellow; 

 others are olive-brown. The beaks are seldom eroded, being 

 thickened there by rlexuous wrinkles remarkable because the 

 rest of the shell is smooth. 



Nacre bluish. The cardinal tooth is compressed, and de- 

 current in shape. 



Being thin, it is crenulate instead of being furrowed (other 

 members of the aubgenus have them furrowed); truncature ob- 

 lique, convex. 



Lateral tooth thin. Muscle scars lightly impressed, confluent 

 behind. 



A small species, at most one and a half inches in altitude. 



(The members of the sub-genus described just previously by 

 Rafinesque are among the largest of the Ohio Naiades. ) 



Altitude of length; diameter T 7 5 . 



Rare in the Ohio, but common in the Kentucky and ad- 

 jacent " petites rivieres." 



While to the writer the above description can be mistaken for nothing 

 else than the Sytnphynota compressa Lea, further evidence seems neces- 

 sary, as Lea quotes one of his friends to the effect that "it equally 

 applies to iris." 



Luckily there remains further evidence which we may ad- 

 duce. Rafinesque, as is well known, divided the Naiades into 

 numerous Genera. These divisions being founded upon the 

 more evident features of the shell, it follows therefore that the 

 contained species of any Genus would naturally sustain a general 

 outward resemblance to each other. 



Rafinesque described this species under the name of Unio 

 (Elliptio) viridift. The Elliptio contained the Unio nigra ; Unio 

 purpureus, Say ; Unio crassa, Say, and a few other shells, all 

 having a general outward similitude, and in such an assemblage the 

 Symphynota, compressa finds congenial associates. 



Rafinesque moreover mentions the fact that the u Unio 

 (Elliptio) leptodon and Unio (Elliptio) frag His" also "resemble" 

 the viridis (with some others'). The reader can easily select speci- 

 mens of the two species mentioned, which resemble the Sym- 

 phynota compressa to a remarkable extent differing, however (as 

 Rafinesque observes), in their teeth. 



