OF THE FAMILY OF NAIADES. 439 



10. Unio Iris. Plate XI. fig. 18. 



Testa angusto-ellipticd, inaquilaterali, sub-ventricosd ; valvulis tenui- 

 bus ; natibus prominulis ; dente cardinali in valvula sinistra, duplici, in 

 dextrd sub-bifido, parvo, erecto ; dentibus lateralibus longis tenuibusque ; 

 margaritd sub-cmruleo-albd. 



Shell narrow-elliptical, inequilateral, slightly ventricose ; valves thin, 

 beaks slightly prominent; cardinal teeth double in the left valve, sub- 

 bifid in the right, small, erect ; lateral teeth long and thin ; nacre bluish 

 white. 



Hab. Ohio. T. G. Lea. 



My Cabinet. 



Cabinet of T. G. Lea. 



Cabinet of Prof. Vanuxem. 



Diam. -5, Length -8, Breadth 1-6 inches. 



Shell long-elliptical, inequilateral, slightly ventricose ; sub- 

 stance of the shell thin, showing the rays through it, rather 

 more dense before than behind ; beaks slightly prominent, 

 approaching, crowned with double concentric undulations 

 when they are not decorticated ; ligament rather long and 

 thin ; epidermis yellowish green, transversely wrinkled, mark- 

 ed with many oblique diverging rays passing from the beaks to 

 the margin : cardinal teeth double in both valves, small, erect, 

 and sharp ; lateral teeth long, bladed, slightly curved and situ- 

 ated on the edge of the margin in contact with the ligament ; 

 anterior cicatrices distinct ; posterior cicatrices confluent and 

 scarcely perceptible ; dorsal cicatrices within the cavity of the 

 beaks, the largest on the under part of the callus ; nacre very 

 thin, milk white anteriorly, bluish white and iridescent pos- 

 teriorly. 



Remarks. — This species most resembles the calceolus. It 

 differs, however, entirely in the teeth, which are distinct and 

 well defined. The calceolus approaches closely to the genus 

 Masmoilonfa of Say. This is less ventricose and possesses 

 more rays. 



VOL.. III. — 5 T 



