DIMYARIA. 137 



pearly, with iridescent reflections. Five inches long. In- 

 habits the Nile. 



Genus 5.— A'iiODO'^T A.— Lamarck. 



Generic Cltaracter. — Equivalve. inequilateral, transverse; 

 hinge linear, without teeth ; an adnate, smooth, cardinal 

 lamina, truncated or forming a sinus at the anterior end, 

 terminating the base of the shell; two lateral, remote, twin, 

 muscular impressions; ligament linear, external, sjink in a 

 cleft at the anterior extremity. 

 The substance of the shell is pearly. 



Anadonta cygnea. — The Swan Anadonta. Plate XVI. 

 fig. 1. Ovate, thin, convex, somewhat compressed on the 

 anterior side ; with concentric wrinkles ; covered wnth a 

 green epidermis, frequently brown towards the umbo ; in- 

 side pearly white ; beaks small and ventricose. Three 

 inches long, and seven broad. Inhabits the fresh- water lakes 

 in Europe. 



Genus 6.— HYRIA.— Zamarcit. 



Generic Character. — Equivalve, oblique, trigonal, eared, 

 with the base truncated and straight, hinge with two spread- 

 ing teeth, the posterior one cleft into numerous divergent 

 portions ; the lateral or anterior tooth strong, elongated, and 

 lamellar ; ligament linear, and external. 



What distinguishes the shells of this genus particularly is the car- 

 dinal or posterior tooth being di\ided into many lamellar plaits, or 

 pieces, the centi-e one being very small. This compoxmd tooth is not 

 erect, but slopes in an inchued position towards the posterior side. 



Hyria avicularis. — The Little-bird Htria. Plate 

 XVI. fig. 2. Umbones smooth and produced, in the form 

 of a tail ; ears large, with pointed terminations ; a greenish- 

 brown epidermis, and finely striated ; inside pearly, and of a 

 rich reddish golden-yellow. Three inches broad. Inhabits 

 the rivers of America. 



