122 CLASS I. TROPIOPODA. ORDER I. BIMUSCULOSA. 



Like the Anodontes, they have a shell entirely destitute of teeth, hut the 

 hinge margin is furnished throughout with a number of thickly-set tuber- 

 cles. In some species, as in the Iridina elongata, Plate XCII. {Spatha 

 elongata, Lea), the hinge-tubercles are almost obsolete ; in others, as in the 

 Iridina ovata, Plate XCIII. {Pleiodon Macmurtriei, Conrad), they are very 

 fully developed. The nearest approach of Anodon to this genus is in the 

 Anodon dipsas (Dipsas plicata, Leach, Cristaria, Schumacher). 



The shell of Iridina may be described as being transverse, nearly cylin- 

 drical, equivalve, inequilateral, covered with an olivaceous epidermis, and 

 the interior is lined with a reddish pearl, exhibiting a more or less iri- 

 descent lustre. The hinge is linear, very long, and somewhat attenuated 

 towards the middle ; there are no teeth, but the margin is furnished with 

 a number of subcrenated, close-set tubercles throughout its entire length. 

 The ligament is marginal and external, and the impression of the posterior 

 adductor muscle is always compound. 



These shells abound in the Nile and other rivers of Africa, and are 

 found in company with tbose of the Galatheea radiata. 



Cailliaud observes, that they are used by the natives of Lower Egypt 

 in preparing flax, and also as spoons for measuring oil, butter, and dif- 

 ferent kinds of provisions. 



Examples. 



PI. XCII. Fig. 1 and 2. 



Iridina elongata, Sowerby, Genera of Shells, No. 7. 

 Anodonta exotica, var., De Blainville. 

 Iridina exotica, var., Deshayes. 

 Spatha elongata, Lea. 



PI. XCIII. Fig. 1 and 2. 

 Iridina ovata, Swainson, Journ. Acad. Nat. Sciences of Philadelphia, 



vol. vii. Part I. pi. 13. Jay's Cat. of Shells, 3rd edit., p. 28. 

 Pleiodon Macmurtriei, Conrad. 



