188 ON THE NAIADES, 



link in the gradual change of the characters of the teeth. It ap- 

 proaches that division of the Naiades which do not possess teeth, more 

 closely than any species which has come under my notice. 



Anodonta lato-marginata. Plate XII. fis;. 34 



'&• 



Tesid obovata, transversa, inxquilaterali ; intus margine latd et cornea ; sinu 

 longo et in partem internam disci vergente; valvulis crassis ; epidermide rubido- 

 fusca ; margarita albd et iridescente. 



Shell obovate, transverse, inequilateral, interior with a broad horn coloured border; 

 sinus long, and pointed towards the interior of the disk ; valves thick ; epidermis red- 

 dish brown ; nacre pearly white and iridescent. 



Hab. River Parana, South America. Dr Burrough. 



My Cabinet. 



Cabinet of the Academy of Natural Sciences of Philadelphia. 



Diam. 1-5, Length 2-5, Breadth 3-5 inches. 



Shell obovate, transverse, inequilateral, inflated, interior with a broad 

 horn coloured border ; sinus long, and pointed to the interior of the 

 disk; substance of the shell thick; beaks somewhat elevated; ligament 

 long and thick; epidermis reddish brown, finely wrinkled, and some- 

 times obscurely rayed; anterior cicatrices distinct; posterior cicatrices 

 confluent; palleal cicatrices almost imperceptible; dorsal cicatrices ap- 

 parently none; cavity of the beaks shallow and subangular; nacre 

 pearly white and iridescent, extending only to the broad horn coloured 

 border. 



Remarks. — In the collection of Dr Burrough there are several spe- 

 cimens of this species, some of which are young and more rotund than 

 that figured here. It presents several characters unusual in the species 

 of this genus, so far as our knowledge extends. The horn coloured 

 border is even broader than that of the tenebrkosu hei'ein described, 

 and the apparent absence of the dorsal cicatrices I have never noticed 

 before in any species of the family. The sinus of this species is very 

 remarkable, as well as that of the tenehricosd. It does not, however, 



